Contents
How the absolute humidity calculator works
Absolute humidity describes the mass of water vapor in a volume of air. This calculator turns temperature and relative humidity into grams per cubic meter; it also shows the saturation value at the same temperature.
How temperature and relative humidity become g/m³
First, the calculator estimates saturation vapor pressure over liquid water with a Magnus approximation. It multiplies that pressure by relative humidity, then converts vapor pressure into vapor density. Fahrenheit input is converted to Celsius before calculation.
WMO Guide to Meteorological Instruments and Methods of Observation
Three temperature and humidity examples
1. At 20 °C and 50% relative humidity, the air contains about 8.62 g/m³ of water vapor. Its saturation value is about 17.24 g/m³.
2. At 0 °C and 80% relative humidity, the result is about 3.88 g/m³. A high percentage can still represent less vapor in colder air.
3. At 30 °C and 50% relative humidity, the result is about 15.13 g/m³. The same 50% describes more vapor than at 20 °C.
What the remaining capacity means
The difference from saturation is a comparison at the entered temperature, not an instruction to add that many grams of water to a room. Heating or cooling changes the saturation value. The model uses saturation over liquid water even below freezing; frost and ice surfaces need a different approximation.
Values are rounded for display; the calculation uses unrounded numbers.
Questions about absolute humidity
Is absolute humidity the same as relative humidity?
No. Absolute humidity is mass per air volume in g/m³; relative humidity is the fraction of saturation at a given temperature.
Can I enter Fahrenheit?
Yes. Select °F; the calculator converts it to Celsius internally without changing the result in g/m³.
What does 100% relative humidity show?
The actual vapor density equals the calculated saturation density at the entered temperature.
Does 0% relative humidity give zero?
Yes, this idealized calculation gives 0 g/m³.
Can I use the remaining capacity to size a humidifier?
Not directly. Room volume, ventilation, temperature changes and ongoing moisture sources also matter.
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