Dew Point Calculator

What this does

A dew point calculator finds the temperature at which air would become saturated and dew, fog, or condensation forms, from the current temperature and relative humidity. Unlike humidity, the dew point is an absolute measure of how much moisture the air holds — the higher it is, the muggier it feels.

How to use it

1. Choose Fahrenheit or Celsius.
2. Enter the air temperature.
3. Enter the relative humidity.
4. Read the dew point and its comfort rating.

How it works

The Magnus-Tetens approximation uses the constants b = 17.625 and c = 243.04°C. It is accurate to within a few tenths of a degree over normal weather conditions. Celsius is used internally and Fahrenheit inputs are converted.

Td = c·γ ÷ (b − γ), γ = ln(RH/100) + bT/(c+T)

Understanding your result

The comfort rating follows the National Weather Service’s summer guide: a dew point of 55°F or lower feels dry and comfortable, 55–65°F becomes sticky with muggy evenings, and 65°F and up means lots of moisture in the air and oppressive conditions. The dew point can never exceed the air temperature — when they are equal the air is fully saturated (100% humidity) and fog or dew forms.

Example

At 68°F (20°C) with 50% humidity, the dew point is about 49°F (9°C), which the tool rates as dry and comfortable.