How relative and absolute humidity are calculated
Relative humidity represents the ratio of actual water vapour pressure to the saturation vapour pressure of air at a given temperature, expressed as a percentage.
Using the Arden Buck formulation, absolute humidity (g/m3) measures the physical mass of water vapour suspended in a cubic metre of air.
Worked example
With an air temperature of 25.0°C and a measured dew point of 15.0°C:
The saturation vapour pressure is 3.169 kPa and actual vapour pressure is 1.705 kPa, giving a relative humidity of 53.8% and an absolute humidity of 12.83 grams per cubic metre.
Inputs for the humidity calculator
Temperature scale
Select whether inputs are entered in Celsius (°C) or Fahrenheit (°F).
Air temperature
Ambient dry-bulb temperature of the air.
Dew point temperature
Measured dew point temperature (must not exceed air temperature).
CALCULATOR QUESTIONS
Humidity calculator questions
Can dew point ever exceed air temperature?
No, relative humidity cannot exceed 100% under normal atmospheric conditions, so the dew point temperature is always less than or equal to the air temperature.
What is absolute humidity?
Absolute humidity is the actual mass of water vapour per unit volume of air (grams of water per cubic metre), regardless of air temperature.