Case 1
- Air temperature
- 25°C
- Relative humidity
- 60%
16.70°C
Open with these valuesDew Point Calculator
16.70°C
Result: 16.70 °CThe dew point is the temperature the air has to reach before its water vapour condenses. It measures moisture directly, so unlike relative humidity it does not move when the air warms or cools. Below about 13 °C the air feels dry; 20 °C and above feels muggy.
Worked examples
Case 2
- Air temperature
- 20°C
- Relative humidity
- 50%
9.26°C
Open with these valuesCase 3
- Air temperature
- 30°C
- Relative humidity
- 80%
26.17°C
Open with these valuesHow it's calculated
Td = c·γ ÷ (b − γ), where γ = ln(RH ÷ 100) + b·T ÷ (c + T)
- StepEnter the air temperature in degrees Celsius.
- StepEnter the relative humidity as a percentage from 1 to 100.
- StepRead the dew point — the temperature at which this air saturates.
- ResultThe closer it sits to the air temperature, the muggier the air feels.
Reference table
| Temperature, humidity | Air | Dew point |
|---|---|---|
| -5, 70 | Cold winter air | -9.63 |
| 15, 15 | Heated room in winter | -11.46 |
| 20, 50 | Comfortable living room | 9.26 |
| 25, 60 | Warm summer day | 16.70 |
| 25, 100 | Saturated — fog | 25.00 |
| 30, 80 | Tropical, oppressive | 26.17 |
Questions
What is the dew point?
The dew point is the temperature to which air must cool, at constant pressure, before its water vapour starts to condense into dew, fog or droplets. It is a direct measure of how much moisture the air holds.
What is the difference between dew point and relative humidity?
Relative humidity is a percentage of what the air could hold at its current temperature, so it changes as the air warms or cools. The dew point is an absolute measure of moisture that does not change with temperature alone, which makes it the more reliable guide.
Why does the dew point equal the temperature at 100 % humidity?
At 100 % relative humidity the air is already saturated, so it does not need to cool at all for condensation to begin. The dew point is therefore the current air temperature, which is the sixth row of the table above.
What dew point feels comfortable?
As a rough guide, a dew point below about 13 °C feels comfortable and dry, values from 16 to 19 °C feel noticeably humid, and 20 °C or more feels oppressive. Because the dew point tracks absolute moisture, it is often a better comfort indicator than relative humidity.
How accurate is the Magnus formula?
It is an empirical fit, not a law of nature: the two coefficients used here were chosen to minimise the largest deviation over the range -40 °C to +50 °C. Several other published sets exist — one widely used pair is quoted at about ±0.35 °C over a similar range — and each gives slightly different answers. That is why this page names the pair it uses.
Sources and last check
Information, not professional advice.