
An SI prefix is a prefix which can be applied to any unit of the International System of Units (SI) to give subdivisions and multiples of that unit. Not all such prefixes are exclusive to SI. Many SI prefixes, and the very idea of using prefixes for this purpose, predate the introduction of the SI in 1960, so they are also quite properly used with many non-SI units. As part of the SI system they are officially determined by the Bureau International des Poids et Mesures. ==Overview== As an example, the prefix ''kilo'' multiplies by one thousand, so a ''kilo''metre is 1,000 metres, and a ''kilo''watt is 1,000 watts. The prefix ''milli'' subdivides by a thousand, so a ''milli''metre is one-thousandth of a metre (1000 millimetres in a metre), and a ''milli''litre is one-thousandth of a litre. The ability to apply the same prefixes to any SI unit is one of the key strengths of the SI, since it considerably simplifies the system's learning and use. See also: Obsolete metric prefixes Examples: * 5 cm = 5 × 10−2 m = 5 × 0.01 m = 0.05 m * 3 MW = 3 × 106 W = 3 × 1 000 000 W = 3 000 000 W Prefixes cannot be combined: for example 10−9 metre must be written as 1 nm, not as 1 mµm. The prefix always takes precedence over any exponentiation; thus "km²" means ''square kilometre'' and not ''kilo–square metre''. For example, 3 km² is equal to 3 000 000 m² and ''not'' to 3000 m² (''nor'' to 9 000 000 m²). Thus the SI prefixes provide steps of a factor one million instead of one thousand in the case of an exponent 2, of a billion in the case of an exponent 3, etc. As a result large numbers may be needed, even if the prefixes are fully used. Prefixes where the exponent is divisible by three are recommended. Hence "100 m" rather than "1 hm". Notable exceptions include centimetre, hectare (hecto-are), centilitre, cubic decimetre (equivalent to one litre), hectopascal, and decibel (one-tenth of a bel). The obsolete prefixes ''myria-'' and ''myrio-'' were dropped before SI was adopted in 1960, probably because they do not fit this pattern, no symbol was available (M, m and µ already being used), and were rarely used anyway. Double prefixes such as ''micromicrofarads'' (picofarads), ''hectokilometres'' (100 kilometres), and ''millimicrons'' or ''micromillimetres'' (both nanometres) were also dropped with the introduction of the SI. The kilogram stands out among all SI base units as the only one that has a prefix. It is derived from the mass of an actual object. The gram is defined as 1/1000 of this object's mass. Though in principle legal, most combinations of prefixes with quantities are very rarely used, even in a scientific or engineering context: * Mass: hectogram, gram, milligram, microgram, and smaller are common. However, megagram or larger are rarely used; tonnes or scientific notation are used instead. Megagram is sometimes used to disambiguate the (metric) tonne from the various (non-metric) tons. * Volume in litres: litre, decilitre, centilitre, millilitre, microlitre, and smaller are common. Larger volumes are sometimes denoted in hectolitres; otherwise in cubic metres or cubic kilometres. * Length: kilometre, metre, decimetre, centimetre, millimetre, and smaller are common. megametre, gigametre, and larger are rarely used. Often used are astronomical units, light years, and parsecs; the astronomical unit is mentioned in the SI standards as an accepted non-SI unit * Time: second, millisecond, microsecond, and shorter are common. The kilosecond and megasecond also have some use, though for these and longer times one usually uses either scientific notation or minutes, hours, and so on. † Britain, Ireland, Australia and New Zealand previously used the long scale number name conventions, but have now at least partly switched to the short scale usage. Note in particular that above a million and below a millionth, the ''same'' name has different values in the two naming systems, so ''billion'' and ''trillion'' (for example) become unfortunately potentially ambiguous terms internationally. Using the SI prefixes can circumvent this problem. ==Pronunciation== The accepted English language pronunciation of the initial G of ''giga'' was once soft, (like ''gigantic''), but now the hard pronunciation, (like ''giggle''), is significantly more common. However, both pronunciations are likely to be understood by most English speakers, though the second is likely to be preferred. == Use outside SI == The symbol "k" is often used to mean a multiple of a thousand, so one may talk of "a 40K salary" (40,000), or the Y2K problem. Note that in these cases an upper case K is often used, although it should be noted that using an uppercase K is never correct when writing under the rules of the SI. Also, it is often used as a prefix to designate the binary prefix kilo = 210 = 1024. === Non-SI units === *Prefixes go back to the introduction of the metric system in the 1790s, long before the SI was introduced in 1960. The prefixes (including those introduced after the introduction of SI) are used with any metric units, SI or not (''e.g.'' millidynes). *SI prefixes rarely appear coupled with imperial units except in some specialised cases (''e.g.'' microinches, kilofeet). *They are also used with other specialized units used in particular fields (''e.g.'' megaelectronvolts, gigaparsecs). *They are also occasionally used with currency units (e.g., gigadollar), mainly by people who are familiar with the prefixes from scientific usage. === Computing === ''Main article: Binary prefix'' The prefixes k and greater are common in computing, where they are applied to information and storage units like the bit and the byte. Since 210 = 1024, and 103 = 1000, this led to the SI prefix letters being (ab-)used to denote "binary" prefixes as follows: ; k:= 210 = 1,024 ; M:= 220 = 1,048,576 ; G:= 230 = 1,073,741,824 ; T:= 240 = 1,099,511,627,776 ; P:= 250 = 1,125,899,906,842,624. However, these prefixes usually retain their powers-of-1000 meanings when used to describe rates of data transmission (bit rates): 10 Mbit/s Ethernet runs at 10,000,000 bit/s, not 10,485,760 bit/s. The problem is compounded by the fact that the units of information (the bit and the byte) are not part of SI, where the bit, byte, octet, baud or symbol rate would rather be given in hertz. Although it is clearer symbology to use "bit" for the bit and "b" for the byte, "b" is often used for bit and "B" for byte. (In SI, B stands for the decibel.) French-speaking countries often use "o" for "octet", nowadays a synonym for byte, but this is unacceptable in SI because of the risk of confusion with the zero. Consequently, the International Electrotechnical Commission (IEC) adopted new binary prefixes in 1998, formed from the first syllable of the decimal prefix plus 'bi' (pronounced 'bee'). The symbol is the decimal symbol plus 'i'. So now, one kilobyte (1 kB) equals 1000 bytes, whereas one kibibyte (1 KiB) equals 210 = 1024 bytes. Likewise mebi (Mi; 220), gibi (Gi; 230), tebi (Ti; 240), pebi (Pi; 250), and exbi (Ei; 260). Although the IEC standard does not mention them, the sequence can be readily extended to zebi (Zi; 270) and yobi (Yi; 280). The adoption of these prefixes has been very limited. ==Proposed extensions== Continuing backwards in the alphabet, after ''zetta'' and ''yotta'', proposals for the next large number include ''xenta'' and ''xona'' (among others), the latter as an alteration of the Latin-derived numerical prefix Wiktionary:nona-, and the next ''small'' number would also start with an x. Preserving the rule on abbreviating the prefixes (a Latin alphabet capital for the large number and a lower-case letter for the small number), even without consensus on the full name the following prefix symbols could be used without ambiguity: X, W, V, x, w, v. The logically next small prefix symbol, "u", is the accepted substitution for "µ" (ISO 2955), the symbol for "micro". However, even some official prefixes may not be understood by all readers, let alone extrapolations of them, so giving an explanation is advisable when using them in communication (as opposed to using them in notes for oneself). Another proposal for xenta/xona is ''novetta'', from the Italian Wiktionary:nove. This does not have the convenience of backward alphabetic order. There are also proposals for further harmonization of the capitalisation. Therefore the symbols for deka, hecto and kilo would be changed from "da", "h" and "k" to "D" or "Da", "H" and "K" respectively. Likewise some lobby for the removal of prefixes that don't fit the 10±3·n scheme, namely hecto, deka, deci and centi. The CGPM has postponed its decision on both matters for now. An unsolved (and maybe unsolvable) issue is the application of prefixes to units with exponents other than ±1. The prefix is always applied before the exponent currently. In volume measuring, for example, this inconvenience has lead to the continued use of the litre, which is one thousandth cubic metre (0.001 m³) or one cubic decimetre (1 dm³), where it could be handy to call it "one milli-cubic metre" ("1 m(m³)")—one cubic millimetre (mm³) is one billionth of a cubic metre. == See also == *binary prefix *engineering notation *number names *orders of magnitude *numbers in various languages (for comparison/etymology) *non-SI unit prefix ==References== ==External links== *[http://www.bipm.fr/en/si/prefixes.html The International Bureau of Weights and Measures (BIPM): SI prefixes] *[http://jimvb.home.mindspring.com/unitsystem.htm Proposal for an extension of the SI-prefix sytem to even larger and smaller units] SI prefixes simple:SI th:หน่วยเอสไอ vi:Hệ đo lường quốc tế
The article claims that a liter is sometimes "referred to as a 'dumphrey'". I couldn't verify that claim and removed it. user:AxelBoldt ------ The powers of two have a new SI standard, IINM. 210 bytes == 1 Kibibyte (1 KiB), 220 bits == 1 Mebibit (1 Mib), 230 bytes = 1 Gibibyte (1 GiB). -- user:Hari (2002-03-18) See http://physics.nist.gov/cuu/Units/binary.html, for instance -- user:Hari (2002-03-18) Could you add an explanation to that effect? Such as "KiB should be used instead of KB...". (It's not a SI standard however.) user:AxelBoldt : Does anyone have an objction to me moving most of the explanation of byte prefixes to Byte prefixes, and leaving just a short paragraph on it here & a link? -- User:Tarquin 14:45 Jan 12, 2003 (UTC) : I've renamed it to "Binary prefixes". It's used for anything based on the power of 2 (e.g., bits, words), not just bytes. -- User:Dwheeler 20:12 21 May 2003 (UTC) In my opinion, the whole "Computing" section must go. It is entirely incorrect when using the rules of the SI. The SI does ''not'' define any special exceptions to do with computing, and this entry implying such is incorrect. It's fine if we move this to a new entry, but it must be very clear that such usage goes against the SI. --User:Eliasen 11:07, 28 Nov 2004 (UTC) :I agree. Remove the section and direct them to binary prefix. - User:Omegatron 22:36, Mar 3, 2005 (UTC) ---- == "iso" prefix == I've just added this. user:Gritchka I have to say I've never seen 'iso' mentioned in this context. What's the authority for this? : I've never heard of it. My encyclopedia doesn't give it in the table of SI. Official reference such as http://physics.nist.gov/Pubs/SP811/sec04.html doesn't give it. The only link I have found on google about it seems contentious (Star Trek science). It's also faintly ludicrous -- a metre is a metre. What is the point of saying "isometre"? Just to clinch it, the official site http://www.bipm.fr/enus/3_SI/si-prefixes.html makes no mention of it. I think someone thought "isobar" was a prefix applied to "bar", whereas it's a line of constant value on a map. In short, I can't find any evidence of its existence, rather, I'm finding evidence of its non-existence. It's going. It's gone ;-) -- User:Tarquin 00:34 Sep 15, 2002 (UTC) == Subdividing these? == It's all very well with the prefixes given here, but what about for example organic chemistry? You require extra endings for 2, 3, 4, 5, 6... (Okay, so they start meth- eth- prop- but-, but that's not the point... think about silane.) What are the prefixes for 1, 2, 3, 4, 5...? : I don't understand your question. There are only prefixes for powers of 10. The prefixes used for systematic chemical names have nothing to do with SI -- User:Tarquin 23:04, 2 Oct 2003 (UTC) == "Billiard", etc == Do the number names "billard", "trilliard", etc, really exist? "Milliard" is old-fashioned (possibly archaic) in UK usage although its cognates are current in some European languages. I have never seen "billiard", etc, listed in any printed dictionary, except as "billiards", which is a game similar to pool. The UK, as has been pointed out on the page, now tends to use "billion", etc, in the same way as they are used in the UK. Other European languages vary between the US system and the older UK system. Could someone point out an authoratitive reference that lists these terms? If not, could I suggest they are removed or marked as neologisms, for the nonce, rare, jokey, or something else? Thanks. -- User:Paul G 09:57, 12 Jan 2004 (UTC) :At least in Swedish, the series Miljon, Miljard, Biljon, Biljard etc. series is used. ----- == Nonna, Dogga, etc. == Is there any reason that Nonabyte and Doggabyte haven't been added to this list yet? I was going to add them myself, but I wanted to clarify that their British name would be "Thousand Quadrillion" and "Quintillion", and that their symbols would be 'N' and 'D'. Does anyone have any authoritative sources on these? -- User:DropDeadGorgias 17:16, 19 Feb 2004 (UTC) :Because they are ''not'' real SI prefixes? -- User:The Anome 06:00, 1 Apr 2004 (UTC) To answer this question about Nona and Dogga, there have been various times in history when nonabyte existed as a Wikipedia article, but it always went onto the "votes for deletion" page. About 90% of all Wikipedians agree that it shouldn't have a Wikipedia article. User:66.245.30.189 02:01, 1 Apr 2004 (UTC) == Prefixes for 10^27 and 10^30 == The creator of the Names of large numbers article has a part that uses SI prefixes for part of it that goes past yotta for xenna and viki. User:66.32.148.174 23:13, 3 Jun 2004 (UTC) == Prefix for 10^27?? == I contacted the webmaster of bimp.org and they say that they will not confirm a prefix for 10^27 as of 2005. Any comments?? User:66.245.95.15 16:29, 2 Jul 2004 (UTC) :Surely the entry for Bronto must be removed until such time as this is confirmed by SI / BIPM? :The BBC has just written an article mentioning Brontobyte http://news.bbc.co.uk/1/hi/magazine/3673262.stm as 10^27, but, Googling, there seems to be few precedents - a Sybase article http://www.sybase.com/content/1031253/EnterpriseUnwired.pdf(which can't even spell yottabyte); a UCL article http://www.ucl.ac.uk/~uczcw11/modules/p028l03.ppt which puts a Brontobyte at 1000 Eb = 10^21 = Zettabyte?? An American article http://openc.k12.or.us/sitedocs/styleguide/abbreviations.html which thinks that Brontobyte = Petabyte = 10^15 - and none of these cite any de jure authority. Does anybody know the origin for this proposed term?? Given the ambiguity, surely it has to go? User:Icairns 23:00, 20 Sep 2004 (UTC) == Bilion == According to billion and Fowler, 'billion' can mean both 10^9 and 10^12 in the UK. Best to not mention it in the table headers -- User:Tarquin 08:57, 21 Sep 2004 (UTC) The 10^12 meaning is utterly obsolete in the whole English-speaking world. As this is the English Wikipedia, the "long scale" column should really be removed to prevent needless confusion. – User:Smyth 13:02, 27 Sep 2004 (UTC) ==Bogus SI prefixes== The category :Category:Bogus SI prefixes contains a whole bunch of stubs that look to me like they're unlikely to grow. Anyone object if I merge them all into Bogus SI prefix or something similar? User:Bryan Derksen 05:33, 14 Oct 2004 (UTC) == Mega == How popular of a belief is it that it is okay to use mega- as a numerical prefix for a million (as if it belonged in the regular Greek numerical prefixes article)?? It is not in there; its literal meaning is "great". User:66.32.255.51 01:29, 31 Oct 2004 (UTC) :Never heard someone use it. Chemicals pentane, hexane, ...., mega-ane? No way, you'd call the latter simply polyethene. I can't think of a situation right now where it could be used. A numerical prefix suggests that it is exact (1,000,000 and not 1,000,002) which usually doesn't make much sense for big numbers. User:Hankwang User_talk:hankwang 12:08, 16 Nov 2004 (UTC) == cc == Do doctors in American medical soap operas always say "cc" (short for "cubic centimetre") to mean "millilitre" because they don't want the audience to know they're using a metric unit? At least here in Finland, "millilitre" is a much more widely known unit than "cubic centimetre", even though they're the same thing. User:JIP — JIP | User talk:JIP 17:17, 1 May 2005 (UTC) :No, all doctors in America use cc. User:Cburnett 17:25, May 1, 2005 (UTC) ::Why do they call it cc instead of millilitres, then? User:JIP — JIP | User talk:JIP 18:52, 1 May 2005 (UTC) :::I wouldn't tak that as an established fact based on one person's comments. For example, what specific context do you have in mind? Liquid drugs are usually labeled in milliliters, and so prescribed. What's used for capacity of syringes? For cranial capacity? The more prevalant usage can be different in different contexts. :::You are probably just a kid who doesn't remember the days when we had to learn that milliliters and cubic centimeters are different units. Some of the usage habits today go back to those days when a distinction was sometimes made for clarity, even though very few measurements were ever precise enough to tell he difference. That's just one of the factors that come into play--but fooling the audience into thinking they are not using a metric units is one of the least plausible factors. Your theory doesn't hold any water. Americans know that it is a metric unit, whether it is "cc" or "cm³" or "mL". User:Gene Nygaard 19:23, 1 May 2005 (UTC) ::::Actually, I've even seen liquid drugs measured in miligrams. In particular, morphine. Measuring liquids in cc's and solids in mg's are probably the most prevalent. I've *never* had a prescription filled in grains or ounces. :) But whatever is used and why, it has little to do with "fooling the audience". User:Cburnett 22:46, May 1, 2005 (UTC) ::::If close to 30 years is "just a kid" to you, then I agree. But no, I don't remember ever learning that cubic centimetres and millilitres are any different. User:JIP — JIP | User talk:JIP 04:27, 2 May 2005 (UTC) :::::From 1901 until 1964, 1 ml was approximately 1.000028 cm³. The liter was then defined as the volume of one kilogram of water at its maximum density, rather than as a cubic decimeter.User:Gene Nygaard 04:40, 2 May 2005 (UTC) ::::::Figures, seeing as I wasn't born in 1964. My parents hadn't even met each other then. The bit about fooling the audience was pure speculation on my part. User:JIP — JIP | User talk:JIP 14:48, 3 May 2005 (UTC) ==Non-standard prefix abbreviations?== What about non-standard abbreviations, such as "mc" or "u" for "micro"? --User:Carnildo 17:41, 20 Jun 2005 (UTC)
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SI prefix
An SI prefix is a prefix which can be applied to any unit of the International System of Units (SI) to give subdivisions and multiples of that unit. Not all such prefixes are exclusive to SI. Many SI prefixes, and the very idea of using prefixes for this purpose, predate the introduction of the SI in 1960, so they are also quite properly used with many non-SI units. As part of the SI system they are officially determined by the Bureau International des Poids et Mesures. ==Overview== As an example, the prefix ''kilo'' multiplies by one thousand, so a ''kilo''metre is 1,000 metres, and a ''kilo''watt is 1,000 watts. The prefix ''milli'' subdivides by a thousand, so a ''milli''metre is one-thousandth of a metre (1000 millimetres in a metre), and a ''milli''litre is one-thousandth of a litre. The ability to apply the same prefixes to any SI unit is one of the key strengths of the SI, since it considerably simplifies the system's learning and use. See also: Obsolete metric prefixes Examples: * 5 cm = 5 × 10−2 m = 5 × 0.01 m = 0.05 m * 3 MW = 3 × 106 W = 3 × 1 000 000 W = 3 000 000 W Prefixes cannot be combined: for example 10−9 metre must be written as 1 nm, not as 1 mµm. The prefix always takes precedence over any exponentiation; thus "km²" means ''square kilometre'' and not ''kilo–square metre''. For example, 3 km² is equal to 3 000 000 m² and ''not'' to 3000 m² (''nor'' to 9 000 000 m²). Thus the SI prefixes provide steps of a factor one million instead of one thousand in the case of an exponent 2, of a billion in the case of an exponent 3, etc. As a result large numbers may be needed, even if the prefixes are fully used. Prefixes where the exponent is divisible by three are recommended. Hence "100 m" rather than "1 hm". Notable exceptions include centimetre, hectare (hecto-are), centilitre, cubic decimetre (equivalent to one litre), hectopascal, and decibel (one-tenth of a bel). The obsolete prefixes ''myria-'' and ''myrio-'' were dropped before SI was adopted in 1960, probably because they do not fit this pattern, no symbol was available (M, m and µ already being used), and were rarely used anyway. Double prefixes such as ''micromicrofarads'' (picofarads), ''hectokilometres'' (100 kilometres), and ''millimicrons'' or ''micromillimetres'' (both nanometres) were also dropped with the introduction of the SI. The kilogram stands out among all SI base units as the only one that has a prefix. It is derived from the mass of an actual object. The gram is defined as 1/1000 of this object's mass. Though in principle legal, most combinations of prefixes with quantities are very rarely used, even in a scientific or engineering context: * Mass: hectogram, gram, milligram, microgram, and smaller are common. However, megagram or larger are rarely used; tonnes or scientific notation are used instead. Megagram is sometimes used to disambiguate the (metric) tonne from the various (non-metric) tons. * Volume in litres: litre, decilitre, centilitre, millilitre, microlitre, and smaller are common. Larger volumes are sometimes denoted in hectolitres; otherwise in cubic metres or cubic kilometres. * Length: kilometre, metre, decimetre, centimetre, millimetre, and smaller are common. megametre, gigametre, and larger are rarely used. Often used are astronomical units, light years, and parsecs; the astronomical unit is mentioned in the SI standards as an accepted non-SI unit * Time: second, millisecond, microsecond, and shorter are common. The kilosecond and megasecond also have some use, though for these and longer times one usually uses either scientific notation or minutes, hours, and so on. † Britain, Ireland, Australia and New Zealand previously used the long scale number name conventions, but have now at least partly switched to the short scale usage. Note in particular that above a million and below a millionth, the ''same'' name has different values in the two naming systems, so ''billion'' and ''trillion'' (for example) become unfortunately potentially ambiguous terms internationally. Using the SI prefixes can circumvent this problem. ==Pronunciation== The accepted English language pronunciation of the initial G of ''giga'' was once soft, (like ''gigantic''), but now the hard pronunciation, (like ''giggle''), is significantly more common. However, both pronunciations are likely to be understood by most English speakers, though the second is likely to be preferred. == Use outside SI == The symbol "k" is often used to mean a multiple of a thousand, so one may talk of "a 40K salary" (40,000), or the Y2K problem. Note that in these cases an upper case K is often used, although it should be noted that using an uppercase K is never correct when writing under the rules of the SI. Also, it is often used as a prefix to designate the binary prefix kilo = 210 = 1024. === Non-SI units === *Prefixes go back to the introduction of the metric system in the 1790s, long before the SI was introduced in 1960. The prefixes (including those introduced after the introduction of SI) are used with any metric units, SI or not (''e.g.'' millidynes). *SI prefixes rarely appear coupled with imperial units except in some specialised cases (''e.g.'' microinches, kilofeet). *They are also used with other specialized units used in particular fields (''e.g.'' megaelectronvolts, gigaparsecs). *They are also occasionally used with currency units (e.g., gigadollar), mainly by people who are familiar with the prefixes from scientific usage. === Computing === ''Main article: Binary prefix'' The prefixes k and greater are common in computing, where they are applied to information and storage units like the bit and the byte. Since 210 = 1024, and 103 = 1000, this led to the SI prefix letters being (ab-)used to denote "binary" prefixes as follows: ; k:= 210 = 1,024 ; M:= 220 = 1,048,576 ; G:= 230 = 1,073,741,824 ; T:= 240 = 1,099,511,627,776 ; P:= 250 = 1,125,899,906,842,624. However, these prefixes usually retain their powers-of-1000 meanings when used to describe rates of data transmission (bit rates): 10 Mbit/s Ethernet runs at 10,000,000 bit/s, not 10,485,760 bit/s. The problem is compounded by the fact that the units of information (the bit and the byte) are not part of SI, where the bit, byte, octet, baud or symbol rate would rather be given in hertz. Although it is clearer symbology to use "bit" for the bit and "b" for the byte, "b" is often used for bit and "B" for byte. (In SI, B stands for the decibel.) French-speaking countries often use "o" for "octet", nowadays a synonym for byte, but this is unacceptable in SI because of the risk of confusion with the zero. Consequently, the International Electrotechnical Commission (IEC) adopted new binary prefixes in 1998, formed from the first syllable of the decimal prefix plus 'bi' (pronounced 'bee'). The symbol is the decimal symbol plus 'i'. So now, one kilobyte (1 kB) equals 1000 bytes, whereas one kibibyte (1 KiB) equals 210 = 1024 bytes. Likewise mebi (Mi; 220), gibi (Gi; 230), tebi (Ti; 240), pebi (Pi; 250), and exbi (Ei; 260). Although the IEC standard does not mention them, the sequence can be readily extended to zebi (Zi; 270) and yobi (Yi; 280). The adoption of these prefixes has been very limited. ==Proposed extensions== Continuing backwards in the alphabet, after ''zetta'' and ''yotta'', proposals for the next large number include ''xenta'' and ''xona'' (among others), the latter as an alteration of the Latin-derived numerical prefix Wiktionary:nona-, and the next ''small'' number would also start with an x. Preserving the rule on abbreviating the prefixes (a Latin alphabet capital for the large number and a lower-case letter for the small number), even without consensus on the full name the following prefix symbols could be used without ambiguity: X, W, V, x, w, v. The logically next small prefix symbol, "u", is the accepted substitution for "µ" (ISO 2955), the symbol for "micro". However, even some official prefixes may not be understood by all readers, let alone extrapolations of them, so giving an explanation is advisable when using them in communication (as opposed to using them in notes for oneself). Another proposal for xenta/xona is ''novetta'', from the Italian Wiktionary:nove. This does not have the convenience of backward alphabetic order. There are also proposals for further harmonization of the capitalisation. Therefore the symbols for deka, hecto and kilo would be changed from "da", "h" and "k" to "D" or "Da", "H" and "K" respectively. Likewise some lobby for the removal of prefixes that don't fit the 10±3·n scheme, namely hecto, deka, deci and centi. The CGPM has postponed its decision on both matters for now. An unsolved (and maybe unsolvable) issue is the application of prefixes to units with exponents other than ±1. The prefix is always applied before the exponent currently. In volume measuring, for example, this inconvenience has lead to the continued use of the litre, which is one thousandth cubic metre (0.001 m³) or one cubic decimetre (1 dm³), where it could be handy to call it "one milli-cubic metre" ("1 m(m³)")—one cubic millimetre (mm³) is one billionth of a cubic metre. == See also == *binary prefix *engineering notation *number names *orders of magnitude *numbers in various languages (for comparison/etymology) *non-SI unit prefix ==References== ==External links== *[http://www.bipm.fr/en/si/prefixes.html The International Bureau of Weights and Measures (BIPM): SI prefixes] *[http://jimvb.home.mindspring.com/unitsystem.htm Proposal for an extension of the SI-prefix sytem to even larger and smaller units] SI prefixes simple:SI th:หน่วยเอสไอ vi:Hệ đo lường quốc tế
SI prefix
The article claims that a liter is sometimes "referred to as a 'dumphrey'". I couldn't verify that claim and removed it. user:AxelBoldt ------ The powers of two have a new SI standard, IINM. 210 bytes == 1 Kibibyte (1 KiB), 220 bits == 1 Mebibit (1 Mib), 230 bytes = 1 Gibibyte (1 GiB). -- user:Hari (2002-03-18) See http://physics.nist.gov/cuu/Units/binary.html, for instance -- user:Hari (2002-03-18) Could you add an explanation to that effect? Such as "KiB should be used instead of KB...". (It's not a SI standard however.) user:AxelBoldt : Does anyone have an objction to me moving most of the explanation of byte prefixes to Byte prefixes, and leaving just a short paragraph on it here & a link? -- User:Tarquin 14:45 Jan 12, 2003 (UTC) : I've renamed it to "Binary prefixes". It's used for anything based on the power of 2 (e.g., bits, words), not just bytes. -- User:Dwheeler 20:12 21 May 2003 (UTC) In my opinion, the whole "Computing" section must go. It is entirely incorrect when using the rules of the SI. The SI does ''not'' define any special exceptions to do with computing, and this entry implying such is incorrect. It's fine if we move this to a new entry, but it must be very clear that such usage goes against the SI. --User:Eliasen 11:07, 28 Nov 2004 (UTC) :I agree. Remove the section and direct them to binary prefix. - User:Omegatron 22:36, Mar 3, 2005 (UTC) ---- == "iso" prefix == I've just added this. user:Gritchka I have to say I've never seen 'iso' mentioned in this context. What's the authority for this? : I've never heard of it. My encyclopedia doesn't give it in the table of SI. Official reference such as http://physics.nist.gov/Pubs/SP811/sec04.html doesn't give it. The only link I have found on google about it seems contentious (Star Trek science). It's also faintly ludicrous -- a metre is a metre. What is the point of saying "isometre"? Just to clinch it, the official site http://www.bipm.fr/enus/3_SI/si-prefixes.html makes no mention of it. I think someone thought "isobar" was a prefix applied to "bar", whereas it's a line of constant value on a map. In short, I can't find any evidence of its existence, rather, I'm finding evidence of its non-existence. It's going. It's gone ;-) -- User:Tarquin 00:34 Sep 15, 2002 (UTC) == Subdividing these? == It's all very well with the prefixes given here, but what about for example organic chemistry? You require extra endings for 2, 3, 4, 5, 6... (Okay, so they start meth- eth- prop- but-, but that's not the point... think about silane.) What are the prefixes for 1, 2, 3, 4, 5...? : I don't understand your question. There are only prefixes for powers of 10. The prefixes used for systematic chemical names have nothing to do with SI -- User:Tarquin 23:04, 2 Oct 2003 (UTC) == "Billiard", etc == Do the number names "billard", "trilliard", etc, really exist? "Milliard" is old-fashioned (possibly archaic) in UK usage although its cognates are current in some European languages. I have never seen "billiard", etc, listed in any printed dictionary, except as "billiards", which is a game similar to pool. The UK, as has been pointed out on the page, now tends to use "billion", etc, in the same way as they are used in the UK. Other European languages vary between the US system and the older UK system. Could someone point out an authoratitive reference that lists these terms? If not, could I suggest they are removed or marked as neologisms, for the nonce, rare, jokey, or something else? Thanks. -- User:Paul G 09:57, 12 Jan 2004 (UTC) :At least in Swedish, the series Miljon, Miljard, Biljon, Biljard etc. series is used. ----- == Nonna, Dogga, etc. == Is there any reason that Nonabyte and Doggabyte haven't been added to this list yet? I was going to add them myself, but I wanted to clarify that their British name would be "Thousand Quadrillion" and "Quintillion", and that their symbols would be 'N' and 'D'. Does anyone have any authoritative sources on these? -- User:DropDeadGorgias 17:16, 19 Feb 2004 (UTC) :Because they are ''not'' real SI prefixes? -- User:The Anome 06:00, 1 Apr 2004 (UTC) To answer this question about Nona and Dogga, there have been various times in history when nonabyte existed as a Wikipedia article, but it always went onto the "votes for deletion" page. About 90% of all Wikipedians agree that it shouldn't have a Wikipedia article. User:66.245.30.189 02:01, 1 Apr 2004 (UTC) == Prefixes for 10^27 and 10^30 == The creator of the Names of large numbers article has a part that uses SI prefixes for part of it that goes past yotta for xenna and viki. User:66.32.148.174 23:13, 3 Jun 2004 (UTC) == Prefix for 10^27?? == I contacted the webmaster of bimp.org and they say that they will not confirm a prefix for 10^27 as of 2005. Any comments?? User:66.245.95.15 16:29, 2 Jul 2004 (UTC) :Surely the entry for Bronto must be removed until such time as this is confirmed by SI / BIPM? :The BBC has just written an article mentioning Brontobyte http://news.bbc.co.uk/1/hi/magazine/3673262.stm as 10^27, but, Googling, there seems to be few precedents - a Sybase article http://www.sybase.com/content/1031253/EnterpriseUnwired.pdf(which can't even spell yottabyte); a UCL article http://www.ucl.ac.uk/~uczcw11/modules/p028l03.ppt which puts a Brontobyte at 1000 Eb = 10^21 = Zettabyte?? An American article http://openc.k12.or.us/sitedocs/styleguide/abbreviations.html which thinks that Brontobyte = Petabyte = 10^15 - and none of these cite any de jure authority. Does anybody know the origin for this proposed term?? Given the ambiguity, surely it has to go? User:Icairns 23:00, 20 Sep 2004 (UTC) == Bilion == According to billion and Fowler, 'billion' can mean both 10^9 and 10^12 in the UK. Best to not mention it in the table headers -- User:Tarquin 08:57, 21 Sep 2004 (UTC) The 10^12 meaning is utterly obsolete in the whole English-speaking world. As this is the English Wikipedia, the "long scale" column should really be removed to prevent needless confusion. – User:Smyth 13:02, 27 Sep 2004 (UTC) ==Bogus SI prefixes== The category :Category:Bogus SI prefixes contains a whole bunch of stubs that look to me like they're unlikely to grow. Anyone object if I merge them all into Bogus SI prefix or something similar? User:Bryan Derksen 05:33, 14 Oct 2004 (UTC) == Mega == How popular of a belief is it that it is okay to use mega- as a numerical prefix for a million (as if it belonged in the regular Greek numerical prefixes article)?? It is not in there; its literal meaning is "great". User:66.32.255.51 01:29, 31 Oct 2004 (UTC) :Never heard someone use it. Chemicals pentane, hexane, ...., mega-ane? No way, you'd call the latter simply polyethene. I can't think of a situation right now where it could be used. A numerical prefix suggests that it is exact (1,000,000 and not 1,000,002) which usually doesn't make much sense for big numbers. User:Hankwang User_talk:hankwang 12:08, 16 Nov 2004 (UTC) == cc == Do doctors in American medical soap operas always say "cc" (short for "cubic centimetre") to mean "millilitre" because they don't want the audience to know they're using a metric unit? At least here in Finland, "millilitre" is a much more widely known unit than "cubic centimetre", even though they're the same thing. User:JIP — JIP | User talk:JIP 17:17, 1 May 2005 (UTC) :No, all doctors in America use cc. User:Cburnett 17:25, May 1, 2005 (UTC) ::Why do they call it cc instead of millilitres, then? User:JIP — JIP | User talk:JIP 18:52, 1 May 2005 (UTC) :::I wouldn't tak that as an established fact based on one person's comments. For example, what specific context do you have in mind? Liquid drugs are usually labeled in milliliters, and so prescribed. What's used for capacity of syringes? For cranial capacity? The more prevalant usage can be different in different contexts. :::You are probably just a kid who doesn't remember the days when we had to learn that milliliters and cubic centimeters are different units. Some of the usage habits today go back to those days when a distinction was sometimes made for clarity, even though very few measurements were ever precise enough to tell he difference. That's just one of the factors that come into play--but fooling the audience into thinking they are not using a metric units is one of the least plausible factors. Your theory doesn't hold any water. Americans know that it is a metric unit, whether it is "cc" or "cm³" or "mL". User:Gene Nygaard 19:23, 1 May 2005 (UTC) ::::Actually, I've even seen liquid drugs measured in miligrams. In particular, morphine. Measuring liquids in cc's and solids in mg's are probably the most prevalent. I've *never* had a prescription filled in grains or ounces. :) But whatever is used and why, it has little to do with "fooling the audience". User:Cburnett 22:46, May 1, 2005 (UTC) ::::If close to 30 years is "just a kid" to you, then I agree. But no, I don't remember ever learning that cubic centimetres and millilitres are any different. User:JIP — JIP | User talk:JIP 04:27, 2 May 2005 (UTC) :::::From 1901 until 1964, 1 ml was approximately 1.000028 cm³. The liter was then defined as the volume of one kilogram of water at its maximum density, rather than as a cubic decimeter.User:Gene Nygaard 04:40, 2 May 2005 (UTC) ::::::Figures, seeing as I wasn't born in 1964. My parents hadn't even met each other then. The bit about fooling the audience was pure speculation on my part. User:JIP — JIP | User talk:JIP 14:48, 3 May 2005 (UTC) ==Non-standard prefix abbreviations?== What about non-standard abbreviations, such as "mc" or "u" for "micro"? --User:Carnildo 17:41, 20 Jun 2005 (UTC)
SI prefix
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SI prefix
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Si prefix
#REDIRECT SI prefix
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