About this tool
The Absolute Humidity Calculator returns the actual mass of water vapor contained in a cubic meter of air, in grams per cubic meter (g/m³). Unlike relative humidity, which is a ratio that changes as air warms or cools, absolute humidity measures the real quantity of water present — the number that matters for drying, curing, museum and archive climate control, and comparing moisture between rooms at different temperatures.
The tool combines the Magnus saturation-vapor-pressure equation with the ideal-gas law: AH = ( 6.112 · exp(17.67·T/(T+243.5)) · RH · 2.1674 ) / (273.15 + T), where T is the air temperature in °C and RH is relative humidity in %. The constant 2.1674 ≈ (molar mass of water, 18.016 g/mol) · 100 / (gas constant, 8.314 J/mol·K), which converts vapor pressure into vapor density.
Everything runs in your browser with no uploads. Enter the temperature (°C or °F) and relative humidity; the result is given in g/m³, mg/m³, and grains per cubic foot (1 g/m³ ≈ 0.437 gr/ft³) for HVAC and imperial workflows. Relative humidity outside 0–100% is rejected as invalid.