The Dew Point Calculator finds the dew point from air temperature and relative humidity, or either of those from the other two values.
Dew point: 57.7 °F = 14.3 °C
| Dew point | 57.7 °F = 14.3 °C |
| Comfort | Comfortable |
The dew point is the temperature to which air must cool to become saturated with water vapour. Below it, water condenses as dew, fog or frost. Unlike relative humidity, the dew point directly measures how much moisture is in the air, so it is a better guide to how muggy it feels.
Using the Magnus approximation: γ = ln(RH/100) + aT/(b + T), dew point = bγ/(a − γ), with a = 17.625 and b = 243.04 °C.
Worked example (defaults): 70 °F (21.1 °C) at 65% humidity gives a dew point of about 57.7 °F (14.3 °C): comfortable.
Below 50 °F (10 °C): dry and pleasant. 50–60 °F: comfortable. 60–65 °F: becoming sticky. 65–70 °F: muggy. Above 70 °F (21 °C): oppressive.
Can dew point exceed temperature? No; when equal, humidity is 100%.
Why do windows fog up? Their surface is below the dew point of indoor air.
What is frost point? The dew point below freezing, where vapour turns directly to ice.