Work out absolute humidity instantly with clear inputs, formula shown and shareable results.
Absolute humidity is the actual mass of water vapour per cubic metre, obtained by applying the ideal gas law to the vapour partial pressure. Air at 25 C and 60% relative humidity holds 19 hPa of vapour, about 13.8 g/m3, with a dew point near 16.7 C. Unlike relative humidity, it does not change when the air is heated.
Vapour pressure
ea = RH / 100 x es(T)
Absolute humidity
AH = ea x M(water) / (R x T)
Because moisture transfer depends on the vapour pressure difference, which relates to absolute rather than relative content.
Grams of vapour per kilogram of dry air. Meteorologists prefer it because it is conserved as air rises and cools.