Relative Humidity Calculator
Enter the air temperature and the dew point temperature.
This result is an estimate only. Double-check important figures before relying on them.
How it is calculated
- RH = 100 × exp(17.625 × Td ÷ (243.04 + Td)) ÷ exp(17.625 × T ÷ (243.04 + T))
- T is the air temperature and Td the dew point, both in °C
For how humid weather feels, use the heat index calculator.
Worked example
Air at 25 °C with a dew point of 15 °C:
- Relative humidity = 53.8%
Why your number may differ
Different constants for the formula give slightly different values. Real measurements also depend on your sensor and on air pressure.
Frequently asked questions
What is relative humidity?
How much water vapour the air holds compared with the most it could hold at that temperature, as a percentage.
What is the dew point?
The temperature to which air must cool for water vapour to start condensing. The closer it is to the air temperature, the more humid it feels.
How accurate is the formula?
The Magnus formula is accurate to well under 1 percentage point for normal weather temperatures.