Dew Point Calculator

Dew point is calculated from air temperature and relative humidity using the Magnus formula (also called the August-Roche-Magnus approximation), the standard method used by the National Weather Service and virtually every weather station. It's accurate to within about 0.35°C (0.6°F) across the range of temperatures found in typical weather.

Dew point is the temperature air would need to cool to (at constant pressure and moisture content) for water vapor to start condensing into liquid water. A higher dew point means more moisture in the air and generally means muggier, more uncomfortable conditions.

When any surface's temperature drops below the dew point, condensation forms on it — this is a key consideration in HVAC design, insulation placement, and preventing moisture damage or mold growth inside walls, on windows, or on cold water pipes.

Relative humidity is a percentage that changes with temperature even if the actual moisture in the air stays the same — the same air can show a different relative humidity at different temperatures. Dew point is a temperature that reflects the actual amount of moisture in the air directly, making it a more consistent measure of how humid it "feels."

Absolute humidity is the actual mass of water vapor in the air, in grams per cubic meter, regardless of temperature. Unlike relative humidity, it doesn't change just because the air warms or cools (as long as no moisture is added or removed) — it's a direct measure of water content, similar in spirit to dew point.

Condensation forms whenever a surface's temperature drops to or below the air's dew point — enter an optional surface temperature (a window, pipe, or wall surface) below to see whether condensation risk applies at your current conditions.