The International System of Units (SI) is made up of 7 base units, featured on this chart with their Measurement League counterparts. The SI, commonly known as the metric system, is easy to use. KILOGRAM (kg) MASS KELVIN (K) TEMPERATURE The kilogram is the unit of mass, The kelvin, unit of thermodynamic equal to the mass of the international temperature, is the fraction 1/273.16 of the prototype of the kilogram (IPK). thermodynamic temperature of the triple point of water. CANDELA (cd) AMPERE (A) LUMINOUS INTENSITY ELECTRIC CURRENT The candela is the luminous The ampere is that constant intensity, in a given direction, current which, if maintained of a source that emits in two straight parallel monochromatic radiation conductors of infinite length, of frequency 540 x 1012 of negligible circular cross hertz and that has a radiant section, and placed 1 meter intensity in that direction of apart in vacuum, would RDIANS OF TH 1/683 watt per steradian. GUA E SI produce between these conductors a force equal to 2 x 10-7 newton per meter of length. METER (m) LENGTH The meter is the length of the path traveled by light in vacuum during a time interval MOLE (mol) of 1/299 792 458 of a second. AMOUNT OF SUBSTANCE The mole is the amount of substance SECOND (s) TIME of a system which contains as many The second is the duration of elementary entities as there are 9 192 631 770 periods of the radiation atoms in 0.012 kilogram of carbon 12. corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. 1 1 1 1 PREFIXES 1 1 This publication 1 01 is free of charge 1 000 00 000 00 000 00 1 000 00 000 00 000 00 000 00 1 000 1 000 1 000 1 000 0. 0. 0. 0. 1 000 1 000 1 0. 1 000 100 10 0.0 0.0 0. 0. 1 000 from: https://doi. 0. org/10.6028/NIST. 10 24 10 21 10 18 10 15 10 12 10 9 10 6 10 3 10 2 10 1 10 0 10 -1 10 -2 10 -3 10 -6 10 -9 10 -12 10 -15 10 -18 10 -21 10 -24 SP.304a-2017 YZEPTGMk hdadc m µ npfazy i a a a a o o o o o ra to nt tt ct ex kilo te ett atto deci milli pic giga peta ept dek ce nano z yo mega yo hec z micr NIST SP 304A femt July 2017 SI symbols are the same worldwide, regardless of the spelling, language, [email protected] www.nist.gov/metric or alphabet. Prefix symbols are used with a unit symbol to represent smaller or larger units by factors that are powers of 10. www.nist.gov.