This dew point calculator finds the temperature at which air becomes saturated and water starts to condense, using air temperature and relative humidity.
Dew point formula
The calculator uses the Magnus approximation with a = 17.62 and b = 243.12°C:
γ = ln(RH ÷ 100) + aT ÷ (b + T) and dew point = bγ ÷ (a − γ)
Worked example
At 77°F (25°C) and 60% relative humidity, the dew point is about 62°F (16.7°C), which most people find sticky.
Frequently asked questions
Why is dew point a better comfort measure than humidity?
Relative humidity changes with temperature during the day, but dew point measures the actual moisture in the air. A dew point above about 65°F (18°C) feels muggy whatever the humidity reading.
Why does condensation form on cold windows?
When a surface is colder than the dew point, the air touching it cools below saturation and water condenses on it.