Dew point calculator
Type the air temperature and its relative humidity: you get the dew point, the temperature below which water vapor condenses.
Result
16.7 °CDew point
- In the other unit
- 62 °F
- Gap with the air temperature
- 8.3 °C
Inputs
- Air temperature
- 25
- Unit
- °C
- Relative humidity
- 60
How it is calculated
Magnus formula: γ = ln(RH ÷ 100) + a T ÷ (b + T), then Td = b γ ÷ (a − γ).
Result
Dew point
- In the other unit
- 62 °F
- Gap with the air temperature
- 8.3 °C
How it is calculated
- Magnus formula: γ = ln(RH ÷ 100) + a T ÷ (b + T), then Td = b γ ÷ (a − γ).
- Constants used: a = 17.62 and b = 243.12 °C (recommended by the WMO, over liquid water).
- °F values are converted to °C before the calculation.
Example
25 °C with 60 % humidity: dew point of 16.7 °C (62.0 °F), so 8.3 °C below the air temperature.
Good to know
- Formula valid from −45 °C to 60 °C, humidity from 1 to 100 %. Accuracy about 0.1 to 0.4 °C.
- Below 0 °C, the frost point (a little higher) is more relevant.
Sources
- WMO, Guide to Instruments and Methods of Observation (WMO-No. 8), Annex 4.B (Magnus formula)
Frequently asked questions
What is this tool used for?
Type the air temperature and its relative humidity: you get the dew point, the temperature below which water vapor condenses.
How is the result calculated?
Magnus formula: γ = ln(RH ÷ 100) + a T ÷ (b + T), then Td = b γ ÷ (a − γ).
What should I check before using the result?
Formula valid from −45 °C to 60 °C, humidity from 1 to 100 %. Accuracy about 0.1 to 0.4 °C.