Absolute humidity calculator
Relative humidity hides how much water is really in the air. Enter the temperature and RH to get absolute humidity in g/m³,grains per pound for HVAC work, and grams per kilogram.
Evidence-checked. Facts and figures on this page are verified against published standards and government sources (Magnus saturation formula + ideal-gas water-vapour density). Last verified July 2026 — our methodology.
Absolute humidity
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- Grains per pound
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- Grams per kilogram
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- Dew point
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Absolute humidity is the mass of water vapour in a cubic metre of air, found from the ideal-gas density of vapour at its actual pressure (saturation pressure at the temperature × RH, via the Magnus formula). Grains per pound (gpp) is the humidity ratio HVAC pros use — grains of moisture per pound of dry air — computed here at sea-level pressure; it reads a little higher at altitude.
Why absolute humidity matters
Two rooms at "50% humidity" can hold very different amounts of water if one is warm and one is cold — because warm air can carry far more. Absolute humidity cuts through that, which is why it tracks comfort and dehumidifier workload better than RH alone. HVAC technicians lean on grains per pound for the same reason. To go from these numbers back to a percentage, use therelative humidity calculator, and to see the temperature the air would need to cool to before it saturates, try thedew point calculator. Background on the concept is indew point vs relative humidity.