Dew Point Calculator — Temperature & Humidity to Dew Point
Enter air temperature and relative humidity to calculate the dew point — the temperature at which air becomes saturated and water vapour begins to condense.
%
Temperature unit
Somewhat uncomfortable (muggy)
- 1
γ factor
ln(60/100) + 17.625 × 25 ÷ (243.04 + 25) = 1.133052Intermediate value linking humidity and temperature in the Magnus approximation. - 2
Dew point
243.04 × 1.133052 ÷ (17.625 − 1.133052) = 16.7
How does this calculator work?
Dew point = (243.04 × γ) / (17.625 − γ), where γ = ln(RH/100) + 17.625·T/(243.04+T). Enter air temperature (−40 to 60 °C) and relative humidity (1–100%) to get the dew point, dew-point depression (T − Td), and a humidity comfort category. Valid for atmospheric conditions; uses Buck (1981) constants.
Formula
How this is calculated
The dew point is the temperature to which air must be cooled (at constant pressure and humidity) for saturation to occur — the point at which relative humidity reaches 100% and condensation begins. Below 0 °C the equivalent is the frost point, where ice crystals rather than liquid water form.
This calculator uses the August-Roche-Magnus approximation with Buck (1981) constants, one of the most widely used and accurate simple formulae for the dew-point calculation. It is valid for temperatures from −40 °C to 60 °C and all physically meaningful relative humidities (1–100%). The formula first computes an intermediate factor γ from the natural log of relative humidity and a temperature-dependent saturation-pressure ratio, then inverts the Magnus relation to get the dew-point temperature.
The "dew-point depression" — the difference between air temperature and dew point — is a useful comfort indicator: a small spread (< 3 °C) means the air is nearly saturated and feels oppressively humid; a large spread (> 15 °C) means the air is dry. A dew point above 21 °C (70 °F) is generally considered uncomfortable by most people. The formula has an error of less than 0.4 °C over the valid range compared to full thermodynamic calculations.
Frequently asked questions
The dew point is the temperature at which air must be cooled, at constant pressure, for water vapour to begin condensing. When a surface — a glass of cold water, grass at dawn, a car roof overnight — drops to the dew-point temperature, condensation (or frost if below 0 °C) forms on it.
Most people find dew points below 10 °C (50 °F) comfortable, 10–16 °C slightly humid, and above 18 °C (65 °F) muggy or uncomfortable. Above 21 °C (70 °F) the air feels oppressive, and above 26 °C (79 °F) conditions become dangerous for outdoor exertion.
Relative humidity is a ratio (%) of current moisture content to the maximum the air can hold at the current temperature — it changes when temperature changes, even if no moisture is added or removed. Dew point is an absolute measure of moisture content: the same dew point at different temperatures can mean very different relative humidities.
Also known as
TG we-Calculate Editorial Team. (2026). Dew Point Calculator — Temperature & Humidity to Dew Point [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/dew-point-calculator
TG we-Calculate Editorial Team. "Dew Point Calculator — Temperature & Humidity to Dew Point." TG we-Calculate. 2026. https://we-calculate.com/calculator/dew-point-calculator.
TG we-Calculate Editorial Team, "Dew Point Calculator — Temperature & Humidity to Dew Point," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/dew-point-calculator
@misc{wecalculate_dew_point_calculator, title = {Dew Point Calculator — Temperature & Humidity to Dew Point}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/dew-point-calculator}}, year = {2026}, note = {TG we-Calculate} }
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