Weather & Climate
Absolute humidity calculator.
Absolute humidity is the mass of water vapour per volume of air. Enter air temperature and relative humidity to get it in g/m³. At 20°C and 50% it is 8.64 g/m³, half of the 17.27 g/m³ the air could hold at saturation.
Air conditions
Absolute humidity
Fill the form and press Calculate.
Worked example
At 20°C the saturation vapour pressure is 23.37 hPa. At 50% relative humidity the vapour pressure is 11.68 hPa. Water vapour density = vapour pressure ÷ (Rv × T) = 1168.5 Pa ÷ (461.495 J/(kg·K) × 293.15 K) = 0.00864 kg/m³, which is 8.64 g/m³. Saturated air (100%) at 20°C holds 17.27 g/m³, and at 30°C it holds 30.35 g/m³.
How it works
Vapour pressure comes from the National Weather Service form of the saturation curve, e = RH × 6.112 × exp[17.67T / (T + 243.5)] hPa. Treating water vapour as an ideal gas, its density is e ÷ (Rv × T) with Rv = 461.495 J/(kg·K) and T in kelvins, converted to grams per cubic metre.
Absolute humidity is distinct from relative humidity: it does not depend on how much the air could hold, only on how much vapour it contains per volume. It changes with temperature and pressure even when no moisture is added or removed.
Sources and basis (all opened 2026-10-08): US National Weather Service El Paso, “Dewpoint and Wet-bulb from Relative Humidity” calculator (page script: es = 6.112 × exp[17.67T / (T + 243.5)], Td = 243.5 ln(e/6.112) / (17.67 − ln(e/6.112))); specific gas constant for water vapour and the ideal-gas form from Wikipedia, Density of air; the definition of absolute humidity as grams of water vapour per cubic metre from Wikipedia, Humidity.
FAQ
What is absolute humidity?
The mass of water vapour per volume of air, usually in grams per cubic metre.
What is the absolute humidity at 20 degrees C and 50% relative humidity?
About 8.64 g/m3. Saturated air at 20 degrees C holds about 17.27 g/m3.
Why does warm air hold more water?
The saturation vapour pressure rises quickly with temperature. Saturated air holds about 17.27 g/m3 at 20 degrees C and about 30.35 g/m3 at 30 degrees C by this calculation.
Is absolute humidity the same as specific humidity?
No. Specific humidity is the ratio of water vapour mass to the total mass of the air parcel, not mass per volume.
How accurate is it?
It uses an approximation of the saturation curve and treats vapour as an ideal gas, which is accurate enough for weather and home use but is not a laboratory standard.
What this calculates, and what it does not
Calculated from published approximations for general information, not a measurement.