Dew point calculator

Enter the air temperature in Celsius or Fahrenheit and the relative humidity. The dew point is the temperature at which that air would become saturated if it cooled at constant pressure and moisture. The tool uses the August–Roche–Magnus approximation: γ = ln(RH/100) + (a·T)/(b+T), then Td = b·γ/(a−γ), with a = 17.625 and b = 243.04 °C (Alduchov and Eskridge). Temperature is converted to Celsius before the formula and back to the scale you chose.

A room at 22 °C and 45% relative humidity has a dew point near 9.5 °C, a spread of about 12.5 °C, which most indoor guides treat as comfortable. The same 22 °C at 70% humidity raises the dew point to about 16 °C and starts to feel humid. At 30 °C and 70% humidity the dew point is near 24 °C: the air is close to saturation and surfaces only a little cooler than the room can fog. A 5 °C night at 90% humidity has a dew point near 3.5 °C; if the ground cools below that, dew is likely.

Comfort bands follow common HVAC planning ranges on the dew point, not a medical scale: under 10 °C dry, 10–16 °C comfortable, 16–18 °C slightly humid, 18–21 °C muggy, 21–24 °C very humid, and above 24 °C oppressive. The spread (air temperature minus dew point) is the margin before condensation. Below 0 °C the result is still a dew point over liquid water, not the frost point over ice, which uses different saturation constants.

Nothing is uploaded. Empty values, temperatures outside −40 to 60 °C, and humidity outside 1–100% are rejected. The heat-index tool estimates how hot the air feels. The scientific temperature tool only converts scales. This one answers when moisture would condense.