Dew point calculator

The dew point is the temperature the air would have to fall to before its moisture condenses. Any surface colder than it will get wet — which is the practical use of the number.

Dew point tells you about comfort far better than relative humidity does, because it is an absolute measure of how much moisture is in the air rather than a percentage of what the air could hold at that temperature. Sixty percent humidity at 10°C and sixty percent at 30°C are completely different experiences; their dew points, 2°C and 21°C, tell you immediately which one is oppressive. Roughly: below 10°C is dry, 13 to 16 is comfortable, 18 to 21 is sticky, and above 21 is unpleasant. The condensation use matters for buildings — if a wall’s inner surface is below the dew point of the room air, it will grow mould, and that is a dew point problem rather than a leak.