What Is Absolute Humidity?

Absolute humidity directly measures how much moisture the air holds — typically expressed as grams of water vapour per cubic metre of air (g/m3). It differs from relative humidity, which expresses moisture as a percentage of the maximum the air could hold at that temperature. Warm air can hold far more moisture than cold air: at 30 degrees Celsius, air can hold about 30 g/m3 of water vapour, but at 0 degrees Celsius, only about 5 g/m3. This is why stepping from a warm, humid bathroom into a cold room can cause condensation — the absolute humidity exceeds what the cooler air can support. Absolute humidity is important in industrial processes (semiconductor manufacturing requires precise moisture control), meteorology (predicting fog and dew), and HVAC design. The dew point — the temperature at which air becomes saturated and condensation begins — directly relates to absolute humidity.