International System of Units SI

The SI is founded on seven SI base units for seven base quantities assumed to be mutually independent.

 SI base units Base quantity Name Symbol length meter m mass kilogram kg time second s electric current ampere A thermodynamic temperature kelvin K amount of substance mole mol luminous intensity candela cd

 Conversion of SI units into British units Quantity Conversion Factor length 1 km = 0·6214 mile = 3281 feet 1m = 3·281 feet = 39·37 inches 1 mm = 0·03937 inches area 1 km2 = 247·1 acres 1 m2 = 10·76 ft2 1 mm2 = 0·00155 in2 volume 1 m3 = 35·32 ft3 1 dm3 = 0·03532 ft3 1 litre = 0·2200 gal mass; weight 1 kg = 2·205 lb 1 g = 0·03527 oz density 1 kg/m3 = 0·06243 lb/ft3 velocity 1 km/h = 0·6214 mile/h 1 m/s = 3·281 ft/s force 1 N = 0·2248 Ibf pressure 1 kN/m2 = 0·1450 lbf/in2 = 20·88 Ibf/ft2 temperature 9/5 °C+32 = °F power 1 kW = 1·341 hp heat flow rate 1 W = 3·412 Btu/h energy 1 J = 0·7376 ft Ibf 1 U = 0·2778 Wh 1 MJ = 0·3726 hp h quantity of heat 1 MJ = 0·2778 kWh 1 kJ = 0·9479 Btu heat content 1 kJ/kg = 0·4299 Btu/lb specific heat 1 kJ/kg°C = 0·2388 Btu/lbºF thermal conductivity 1 W/m°C = 6·935 Btu in/ft2hºF thermal conductance 1 W/m2ºC = 0·1761 Btu/ft2hºF

 Prefixes 10 exp 24 yotta Y 1.000.000.000.000.000.000.000.000 10 exp 21 zetta Z 1.000.000.000.000.000.000.000 10 exp 18 exa E 1.000.000.000.000.000.000 10 exp 15 peta P 1.000.000.000.000.000 10 exp 12 tera T 1.000.000.000.000 10 exp 9 giga G 1.000.000.000 10 exp 6 mega M 1.000.000 10 exp 3 kilo k 1.000 10 exp 2 hecto h 100 10 deka da 10 1 1 10 exp -1 deci d 0.1 10 exp -2 centi c 0.01 10 exp -3 milli m 0.001 10 exp -6 micro u 0.000 001 10 exp -9 nano n 0.000 000 001 10 exp -12 pico p 0.000 000 000 001 10 exp -15 femto f 0.000 000 000 000 001 10 exp -18 atto a 0.000 000 000 000 000 001 10 exp -21 zepto z 0.000 000 000 000 000 000 001 10 exp -24 yocto y 0.000 000 000 000 000 000 000 001

SI derived units
The so called derived quantities are defined in terms of the seven base quantities via quantity equations. The SI derived units are obtained from the seven SI base units.

 some SI derived unit Name Symbol area square meter m2 volume cubic meter m3 speed, velocity meter per second m/s acceleration meter per second squared m/s2 wave number reciprocal meter m-1 mass density kilogram per cubic meter kg/m3 specific volume cubic meter per kilogram m3/kg current density ampere per square meter A/m2 magnetic field strength ampere per meter A/m amount-of-substance concentration mole per cubic meter mol/m3 luminance candela per square meter cd/m2 mass fraction kilogram per kilogram, which may be represented by the number 1 kg/kg = 1

 SI derived units with special names and symbols SI derived unit Name Unit Units Units frequency Hertz Hz - s-1 power, radiant flux Watt W J/s m2·kg·s-3 electric charge, quantity of electricity Coulomb C - s·A electric potential difference, electromotive force Volt V W/A m2·kg·s-3·A-1 capacitance Farad F C/V m-2·kg-1·s4·A2 electric resistance Ohm V/A m2·kg·s-3·A-2 electric conductance Siemens S A/V m-2·kg-1·s3·A2 force Newton N - m·kg·s-2 pressure, stress Pascal Pa N/m2 m-1·kg·s-2 energy, work, quantity of heat Joule J N·m m2·kg·s-2 magnetic flux Weber Wb V·s m2·kg·s-2·A-1 magnetic flux density Tesla T Wb/m2 kg·s-2·A-1 inductance Henry H Wb/A m2·kg·s-2·A-2 luminous flux Lumen lm cd·sr (c) m2·m-2·cd = cd illuminance Lux lx lm/m2 m2·m-4·cd = m-2·cd