Dew Point Calculator
Calculate the dew point from temperature and relative humidity.
Tip: A dew point above 20°C makes sleep difficult — use the air conditioner in 'dry' mode or a dehumidifier for comfort at night.
Did this tool help?
About this digital tool
The dew point calculator finds the temperature at which water vapour condenses, from the air temperature and relative humidity. Enter the temperature in °C and the humidity in %, and get the dew point and an estimate of the comfort level.
The tool uses the Magnus formula: γ = ln(RH ÷ 100) + 17.625 × T ÷ (243.04 + T), and the dew point is 243.04 × γ ÷ (17.625 − γ). The closer the dew point is to the temperature, the more humid the air. The feel runs from very comfortable (below 10°C) to very humid (above 21°C). It is useful for predicting fog and dew, for checking condensation on walls and windows and for comfort at home.
How to use
- Enter the current temperature (°C)
- Enter the relative humidity (%)
- See the dew point
- See the comfort level
- See the temperature below which condensation would form
Frequently asked questions
What does the dew point show?
It shows how much moisture the air really holds, regardless of temperature. A relative humidity of 50% at 20°C and 50% at 35°C have very different absolute humidity — the dew point reveals this.
Why is it more useful than relative humidity?
Relative humidity depends on temperature: 80% at 15°C (comfortable) ≠ 80% at 32°C (unbearable). The dew point gives absolute values: a 10°C dew point = always comfortable, 22°C = always humid.
When do dew or fog form?
When the air temperature falls to the dew point, vapour condenses: dew (on surfaces), fog (in the air). If the dew point is < 0°C, frost forms instead of dew.
What happens when the temperature falls below the dew point?
Water vapour condenses into water droplets. This is seen as dew on grass, fog in the air or condensation on cold windows and walls.