Dew point is a better comfort guide than relative humidity: above about 20 °C most people feel muggy.
How to use the Dew Point Calculator
- Air temperature
- Relative humidity
Results update as you type, and every field accepts the units shown in its menu.
How it works
The Magnus approximation relates saturation vapour pressure to temperature.
Inputs explained
| Field | What to enter |
|---|---|
| Air temperature | Units: °C, °F, K |
| Relative humidity | In % |
Example values
How the main result changes when Air temperature changes and everything else stays at the example values above:
| Air temperature (°C) | Dew point (°C) |
|---|---|
| 12.5 | 4.9 |
| 18.75 | 10.8 |
| 25 | 16.7 |
| 31.25 | 22.6 |
| 37.5 | 28.4 |
| 50 | 40.1 |
Formula
γ = ln(RH ÷ 100) + b T ÷ (c + T)Dew point = c γ ÷ (b − γ), b = 17.62, c = 243.12 °CWorked example
Inputs — Air temperature: 25 °C; Relative humidity: 60 %.
Results — Dew point = 16.7 °C.
Frequently asked questions
Why does dew form at night?
Surfaces cool below the dew point and water condenses on them.
Can dew point exceed air temperature?
No; when they are equal, humidity is 100%.
What formula does the Dew Point Calculator use?
γ = ln(RH ÷ 100) + b T ÷ (c + T).