Dew point calculator
Enter temperature and humidity to get the dew point, a handy measure of comfort and of condensation risk on walls and windows.
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How to use it
- Enter air temperature, temperature unit and relative humidity.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
γ = ln(RH ÷ 100) + aT ÷ (b + T), then Td = bγ ÷ (a − γ), with the Alduchov and Eskridge coefficients a = 17.625 and b = 243.04°C.
Example
Inputs: Air temperature = 25, Temperature unit = Celsius (°C), Relative humidity = 60 %. Result: Dew point: 16.7 °C; In the other unit: 62.1 °F; Temperature minus dew point: 8.3 °C.
Limits and caveats
- The Magnus formula is accurate to about 0.1°C in normal weather, over water rather than ice.
- Assumes air pressure near sea level.
Questions about this tool
What dew point feels comfortable?
Below about 13°C most people feel comfortable; above 20°C the air feels oppressive.
How is dew point different from relative humidity?
Dew point tracks the actual amount of vapour, while relative humidity changes with temperature even when the vapour stays the same.
When do dew or fog form?
When the temperature falls to the dew point and vapour condenses on surfaces or in the air.