Français | 简体中文 | 繁體中文 This Web Site uses UTF-8 encoding. 2005-04-07 SI units SI prefixes Units outside the SI Use the International System of Units (US) The United States uses different names for certain units and prefixes. Sources: International Bureau of Weights and Measures (BIPM): SI United States: National Institute of Standards and Technology: SI
SI base unit Symbol Name Base quantity m metre; US: meter length kg kilogram mass s second time A ampere electrical current K kelvin thermodynamic temperature mol mole amount of substance cd candela luminous intensity The mass is commonly called the weight in people's daily life and trade. (The word weight denotes a quantity of the same nature as a force.)
SI derived unit Symbol Name Derived quantity m2 square metre area m3 cubic metre volume m/s metre per second speed, velocity m/s2 metre per second squared acceleration m-1 reciprocal metre wavenumber kg/m3 kilogram per cubic metre density, mass density m3/kg cubic metre per kilogram specific volume A/m2 ampere per square metre current density A/m ampere per metre magnetic field strength mol/m3 mole per cubic metre concentration (of amount of substance) cd/m2 candela per square metre luminance 1 (the number) one refractive index m3/s cubic metre per second volume flow rate kg/s kilogram per second mass flow rate m2/s square metre per second kinematic viscosity m3 metre to the power of three section modulus m3/mol cubic metre per mole molar volume
SI derived unit Symbol Name Derived quantity rad radian plane angle sr steradian solid angle Hz hertz frequency N newton force Pa pascal pressure, stress J joule energy, work, quantity of heat W watt power, radiant flux C coulomb electric charge, quantity of electricity V volt electric potential difference, electromotive force F farad capacitance Ω ohm electric resistance S siemens electric conductance Wb weber magnetic flux T tesla magnetic flux density H henry inductance °C degree Celsius Celsius temperature lm lumen luminous flux lx lux illuminance Bq becquerel activity (referred to a radionuclide) Gy gray absorbed dose, specific energy (imparted), kerma Sv sievert dose equivalent, ambient dose equivalent, directional dose equivalent, personal dose equivalent, organ equivalent dose kat katal catalytic activity
SI derived unit Symbol Name Derived quantity Pa . s pascal second dynamic viscosity N . m newton metre moment of force N/m newton per metre surface tension rad/s radian per second angular velocity rad/s2 radian per second squared angular acceleration W/m2 watt per square metre heat flux density, irradiance J/K joule per kelvin heat capacity, entropy J/(kg . K) joule per kilogram kelvin specific heat capacity, specific entropy J/kg joule per kilogram specific energy W/(m . K) watt per metre kelvin thermal conductivity J/m3 joule per cubic metre energy density V/m volt per metre electric field strength C/m3 coulomb per cubic metre electric charge density C/m2 coulomb per square metre electric flux density F/m farad per metre permittivity H/m henry per metre permeability J/mol joule per mole molar energy J/(mol . K) joule per mole kelvin molar entropy, molar heat capacity C/kg coulomb per kilogram exposure (x and γ rays) Gy/s gray per second absorbed dose rate W/sr watt per steradian radiant intensity W/(m2 . sr) watt per square metre steradian radiance kat/m3 katal per cubic metre catalytic (activity) concentration C/(kg . s) coulomb per kilogram second exposure rate Sv/s sievert per second dose equivalent rate S/m siemens per metre electrical conductivity S . m2/mol siemens square metre per mole molar conductivity
Factor Symbol Prefix 1024 Y yotta 1021 Z zetta 1018 E exa 1015 P peta 1012 T tera 109 G giga 106 M mega 103 k kilo 102 h hecto 101 da deca; US: deka 10-1 d deci 10-2 c centi 10-3 m milli 10-6 µ micro 10-9 n nano 10-12 p pico 10-15 f femto 10-18 a atto 10-21 z zepto 10-24 y yocto
Symbol Name Non-SI units accepted for use with the International System min minute h hour d day ° degree ' minute " second l, L litre; US: liter t tonne; US: metric ton Np neper B bel dB decibel Non-SI units accepted for use with the SI, whose values in SI units are obtained experimentally eV electronvolt u unified atomic mass unit ua astronomical unit Other non-SI units currently accepted for use with the International System nautical mile knot a are ha hectare bar bar Å ångstöm b barn Other non-SI units erg erg dyn dyne P poise St stokes G gauss Oe oersted Mx maxwell sb stilb ph phot Gal gal Ci curie R röntgen rad rad rem rem X unit γ gamma Jy jansky fermi metric carat Torr torr atm standard atmosphere cal calorie µ micron
The International System of Units (SI) is the modern metric system and adopted by the International Organization for Standardization (ISO) as International Standard ISO 1000.
The United States signed the Convention of the Metre (Meter Convention in American English) in 1875, but limited use of the SI and overuse of the inch-pound units cause obstacles. The United States is not yet seriously committed to metrication and some resistances exist. The International System of Units is the only official name of the modern metric system, but the inch-pound units are called variously. Paul TRUSTEN, a registered pharmacist in Texas in the United States, has devised an acronym WOMBAT (Way Of Measuring Badly in America Today) for the inch-pound units and the like. Another interpretation not from him is Waste Of Money, Brain, And Time.
The United Kingdom is widely metricated, but resistance exists and metric road signs are usually illegal. Metric traffic signs in the United States are legal but not required unless a state law says otherwise, though the inch-pound units still prevail. Canada is mostly metricated, but its metrication is incomplete in a few cases.
The SI is easy to use, but many people in the United States and the United Kingdom claim that they do not understand the SI. Most people know the decimal relations of common units of the SI, but even people against the SI may not know the chaotic relations of the inch-pound units. They may not know how many yards or feet in a mile, how many acres in a square mile, how many cubic inches in a gallon, or how many pounds in a ton.
Some people are hostile toward the SI. Many news media against the SI convert original values of the SI to the inch-pound units. Some people attempt to smuggle the inch-pound units to countries and areas where they are illegal.
Globalization requires the SI as the uniform system. People against the SI who claim denial of freedom of choice must consider how hard it is to handle the inch-pound units. Freedom must have a limit or conflicts will occur.
External links FR France: Louis JOURDAN: La grande métrication GB United Kingdom (UK): UK Metric Association UKMetrication.com KryssTal: The Metric System A Dictionary of Measures, Units and Conversions by Frank TAPSON US United States: U.S. Metric Association SI Navigator James R. FRYSINGER: SI Guide Metric 4 US Tom J. PRICE: Metric, Once and For All Russ ROWLETT: A Dictionary of Units of Measurement Make the Metric System Standard In the USA Petition Yahoo! Groups: metricamerica