And many search engines can do unit conversions for you. There are many unit conversion sites online, as well as smartphone apps do a search for them. In the 1970s, various companies made cardboard or plastic “slide” converters, but as far as we know, they exist only as antiques these days. Some handheld calculators can do unit conversions, but we don’t keep a list of model numbers.
For a (very) comprehensive list of conversion factors, get a copy of NIST Special Publication 811, which you can download from the NIST SI bibliography, and see Appendix B. Here’s a list of the most frequently used conversion factors. Where can I find unit conversion factors or calculators? You’ll see it (and a few other obsolete units) listed in the original tables in the Metric Act of 1866. Long ago, there was a prefix for a factor of 10 000 (10 4), “myria”, but that is long obsolete and not used in the SI. SI prefixes are defined for powers of 1000 - i.e., 10 n where n is a multiple of 3 - as well as 10 ☑ and 10 ☒. Where can I get a list of SI prefixes and their origins?įor a complete list of the SI prefix names and symbols, with their factors, pronunciations, and origins, see SI prefixes and their etymologies. We also have a more complete list of SI reference publications from various sources. In addition, there’s IEEE/ASTM SI 10-2016, American National Standard for Metric Practice, which is available for purchase from ASTM or from Techstreet. These and others are available via the SI bibliography at NIST. You might also want NIST SP 330, The International System of Units (SI), which is the US version of the SI Brochure, and SP 811, Guide for the Use of the International System of Units (SI), which has much more detail on usage. It’s available at no charge in English or French. To read the SI standard, get a copy of the SI Brochure from the International Bureau of Weights and Measures (BIPM). Refer to the question What’s a metric? (below) for other meanings of the word. People sometimes use “metric” or “metrics” as slang for “the metric system”, but this is not technically correct. Note that “metric” (in the context of the SI) is an adjective, not a noun: metric system, metric units, metric legislation, metric conversion, metric ton, etc. So, in the early days, the term “metric system” was ambiguous, leading to the term “modern metric system” to refer specifically to the SI.īut it’s been more than 50 years since the SI was defined, so for all practical purposes, today “the metric system” is synonymous with the SI. For example, the CGS system used the centimetre, gram, and second, and included now-obsolete units like the erg and dyne. The latter terms are used primarily in formal contexts.īefore the SI, there were older forms of the metric system that used different base units. “The metric system” is a nickname for the International System of Units, aka the SI. Generally, when used as a noun the abbreviation “SI” is preceded by the: “In the SI, the value of the velocity of light in vacuum is c = 299 792 458 m/s exactly.” Is there a difference between “the metric system” and the SI? But it’s useful to have a standard, international abbreviation, and that’s “SI” (all caps, no periods, pronounced as separate letters “ess eye”), derived from the French Système international d’unités but used in all languages. The name “The International System of Units” is, of course, translated appropriately in different languages. “mass” Is the International System of Units called “SI” in all languages? How can I type unit symbols such as m 2, ☌, N⋅m, and µm?.Does an exponent apply to the prefix as well as the unit?.How do you write units derived by multiplication or division?.How do you handle fractions of a metric unit?.What about the decimal point? I’ve seen a comma instead of a period.How about commas to separate groups of three digits?.Should there be a space between the number and a unit symbol?.Why does the base unit for mass, the kilogram, have a numeric prefix?.What about atmospheric pressure: hectopascals, kilopascals?.What about angles? Radians, steradians, degrees, ….Is it “kelvins” or “degrees Kelvin”? Celsius? Centigrade?.What about “K” for computer-related terms?.Is the litre the same as a cubic decimetre?.Are they spelled “metre” and “litre” or “meter” and “liter”?.How do you capitalize, abbreviate, and pluralize unit names and symbols?.Where can I find unit conversion factors or calculators?.Where can I get a list of SI prefixes and their origins?.How can I get a copy of the SI standard?.Is there a difference between “the metric system” and the SI?.Is the International System of Units called “SI” in all languages?.