Absolute Humidity Calculator

Absolute humidity is the actual mass of water vapor present in a fixed volume of air, independent of temperature. It is reported here in grams of water per cubic meter, so a reading of 13.82 g/m3 means every cubic meter of that air carries about 13.82 grams of water.

Relative humidity is a percent of the maximum vapor the air can hold at its current temperature, so it shifts as the air warms or cools. Absolute humidity is the real amount of vapor present. At the same relative humidity, warmer air holds a lot more water, which is why 60 percent at 30 C feels heavier than 60 percent at 10 C.

It uses AH = (6.112 * exp((17.67*T)/(T+243.5)) * RH * 2.1674) / (273.15 + T), where T is Celsius and RH is a percent. The 6.112 hPa term is the saturation vapor pressure at 0 C from the Magnus approximation, and 2.1674 converts hectopascals to g/m3 through the ideal gas law for water vapor.

Relative humidity must be greater than 0 and at most 100. A value of 0 or any number above 100 is rejected with an error, since 0 percent has no vapor to measure and readings over 100 percent describe supersaturated air the simple formula does not model.

Yes. Any finite temperature is accepted, including sub-zero winter values and hot summer values. The Magnus approximation stays accurate across roughly -40 C to 50 C, which covers almost every real weather and indoor condition.

Higher temperatures raise the saturation vapor pressure, so warmer air can carry more water before it condenses. That is why the same relative humidity produces a much larger absolute humidity on a hot day, and why cooling humid air past its dew point squeezes out droplets.

Comfortable indoor air often sits around 7 to 12 g/m3. Very dry heated winter air can fall below 5 g/m3, which dries out skin and airways, while hot tropical air can climb past 25 g/m3.

The calculator rounds internally to nine decimal places and the display shows up to two decimals, so 25 C at 60 percent reads 13.82 g/m3. It is an engineering approximation, not a laboratory measurement, but it agrees with reference tables to well under one percent in ordinary conditions.

Yes. The calculation runs entirely in your browser with JavaScript, and nothing you type is sent to a server or stored. You can use it offline once the page has loaded.