Système International d'Unités (SI units)

Prefixes (To multiply a unit by a factor)

Base units

LENGTH (metre). 1 m = 1000 mm = 39.37 inches = 3.281 ft = 1.094 yd

1 in = 25.4000 mm. 1/1000 in = 25.4 µm. 1 mile = 1.609 344 km exactly

MASS (kilogram). 1 kg = 2.2046 lb. 1 Mg = 1 tonne = 1000 kg = 0.9842 ton

TIME (second). 86400 s = 1440 min = 24 h = 1 d

ELECTRIC CURRENT (ampere). 1 A x 1 volt (V) x power factor = 1 watt (W)

TEMPERATURE (kelvin, degree Celsius). 273.15 K = 0 °C = 32 °F. [K=°C+273.15]

AMOUNT OF SUBSTANCE (mole). 1 mol = as many entities as atoms in 12 g of carbon-12.

LUMINOUS INTENSITY (candela). 1 cd used to be candlepower, about 0.02 W.

Supplementary units

PLANE ANGLE (radian). 1 rad =180/π degrees = 57° 17' 44.8"

SOLID ANGLE (steradian). 1 sr = 1 m² on 1 m radius sphere

Derived units

AREA (square metre, hectare). 1 m² = 1 000 000 mm² = 1550 in² = 1.196 yd²

1 ha = 10 000 m² = 2.471 acres

VOLUME (cubic metre, litre). 1 m³ = 1000 l = 220.0 UK gallons = 1.308 yd³ =35.315 ft³.

1 litre of water at 4 °C has a mass of 1 kg =1.76 pints..

1 litre of water at 20 °C has a mass of 0.998 kg.

DENSITY and CONCENTRATIONS (kilogram per cubic metre). 1 kg/m³ = 1.686 lb/yd³

VELOCITY (metre per second). 1 m/s = 3.6 km/h = 2.237 miles per hour

FORCE (newton), 1 N = 1 kg m/s² = 0.2248 lbf. 10 kN = 1.004 tonf

(1kg exerts a force of 9.81 N in the British Isles)

ENERGY (joule). 1 J = 1 Ws = 1 Nm = 0.7373 ft lbf = 0.0002388459 nutritional calories.

1 kJ = 0.94781 Btu = 2391.6 20 °C Calories.. 3.6 MJ = 1 kWh.

PRESSURE, STRESS & MODULUS OF ELASTICITY (newton per square metre, pascal, bar).

1 000 000 N/m² = 1000 kN/m² = 1 N/mm² = 1 MN/m² = 1 MPa = 10 bar = 145 lbf/in²

POWER (watt). 1 W = 1 J/s = 0.00134 horse power

THERMAL CAPACITY (joule per kilogram kelvin).

Value for water = 4181.3 J/kg K at 20 °C. Steel = 475 J/kg K (3700 J/litre K). Aggregates 900 J/kg K.

THERMAL CONDUCTIVITY (watt per metre degree Celsius). 1 W/m °C = 6.933 Btu/ft² h °F

THERMAL CONDUCTANCE (watt per square meter degree Celsius).

1 W/m² °C = 44.4 cal/ft² °F h = 0.08 k cal/ft² °C h = 0.1761 Btu/ft² h °F ("U" value)

LUMINOUS FLUX (lumen). 1 lm = 1cd sr = 0.0016 W of visible light

ILLUMINATION (lux). 1 lx = 1 lm/m².

FREQUENCY (hertz). 1 Hz = 1 cycle/s. Frequency (GHz) = Light speed (m/s) / wave length (nm)

SPEED of light = 299 792 458 m/s exactly. Note: Prefixes equidistant up & down from base m/s.

For more detail see http://en.wikipedia.org/wiki/SI#Units