Prefixes

Units can be used as such or in multiples or fractions of ten:

1 m = 100 cm = 1000 mm
1 m² = 10 000 cm² = 10⁶ mm²
1 m³ = 10⁶ cm³ = 10⁹ mm³
1 Mg m^-3 = 10³ kg m^-3 = 1 g cm^-3
1 kPa = 10 mbar
1 joule = 0.2388 cal
1 watt = 1 J s-1 = 0.8598 kcal h^-1
1 W m^-2 = 0.8598 kcal m^-2 h^-1
1 W m^-2 = 1.433 × 10^-3 cal cm^-2 min^-1
1 Hp = 745.7 W
1 W = 0.001431 Hp
Water flow (m³ s^-1) = 0.55 × Pump power (W)/Pressure (kPa)
Water flow (litre s^-1) = 5.43 × Pump power (kilowatts)/pressure (bars)

Brake Horsepower is the horsepower for an electric motor. Do not use for fuel-powered engines.

Conversion factors

Temperature

Standard unit: degree Celsius (°C)

Pressure (air pressure, vapour pressure)

Standard unit: kilopascal (kPa)

Wind speed

Standard unit: metre per second (m s^-1)

Radiation

Standard unit: megajoule per square metre and per day (MJ m² day^-1) or as equivalent evaporation in mm per day (mm day^-1)

Physical properties

Properties of Water

T = temperature, r_w = density of water and l = latent heat of vaporization

Properties of gases at P_b = 101.3 kPa barometric pressure

T= temperature and r = density

Black body emittance (W m^-2) as a function of subzero temperature (°C)