Enter a temperature and relative humidity to calculate the dew point.
How to Use the Dew Point Calculator
Type in the current temperature — flip the °C/°F toggle first if your source reports Fahrenheit and you'd rather work in that unit — then enter the relative humidity percentage. Both fields recalculate the dew point on every keystroke; there's nothing to submit.
Dew point is the temperature air would have to cool to before it's fully saturated and starts condensing out as dew, fog, or frost. That's a different measurement than relative humidity, which describes how close the air is to saturation at its current temperature — a number that swings through the day even when the actual water content of the air hasn't moved at all. Cool the air overnight without adding or removing moisture and relative humidity climbs toward 100%, not because it got more humid but because cold air simply holds less water before saturating. Dew point tracks the water content directly, which is why meteorologists lean on it as the more honest answer to "how humid does it actually feel."
The Magnus-Tetens Approximation
This calculator uses the Magnus-Tetens approximation, a standard meteorological formula for estimating dew point across the range of temperatures and humidities found at Earth's surface:
α = ln(RH ÷ 100) + (17.27 × T) ÷ (237.7 + T)
Td = (237.7 × α) ÷ (17.27 − α)T is temperature in Celsius, RH is relative humidity as a percentage, and 17.27 and 237.7 are the formula's standard coefficients — fixed constants, not adjustable settings. Fahrenheit input gets converted to Celsius before the formula runs, then the result converts back if that's the display unit selected.
Dew point can never exceed the actual air temperature. When the two meet, the air is fully saturated — relative humidity effectively hits 100%, and fog or dew starts forming.
Reading the Comfort Scale
Meteorologists commonly cite dew point thresholds for how muggy a day will feel — not a hard scientific boundary, just an informal scale that's stuck around because it holds up in practice:
- Below 55°F (13°C): dry, comfortable air.
- 60–65°F (16–18°C) starts feeling noticeably humid on a walk outside.
- Above 70°F (21°C) is the oppressive range — exertion outdoors gets unpleasant no matter what the thermometer says.
A 90°F day with a 50°F dew point feels dramatically different from a 90°F day with a 75°F dew point, even though the air temperature reading is identical. That gap is exactly what relative humidity alone can't show you.