Dew Point Calculator
Calculate the dew point — the temperature at which air would need to cool to reach 100% humidity.
How to use the Dew Point Calculator
- Enter your inputs into the Dew Point Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The Magnus-Tetens approximation
γ(T, RH) = ln(RH/100) + (b·T)/(c+T) · · · Dew point = c·γ / (b − γ)
T in °C, RH in %, with constants b = 17.625 and c = 243.04. Accurate to within 0.4°C for temperatures −45°C to 60°C.
Worked example
At 25°C (77°F) with 60% relative humidity: dew point ≈ 16.7°C (62°F). At 30°C and 80% RH: dew point ≈ 26.2°C (79°F) — uncomfortably high; air feels muggy and dripping.
Frequently asked questions
Why is dew point important?
Dew point is an absolute measure of humidity (unlike relative humidity, which varies with temperature). Dew points above 65°F feel humid; above 75°F feel oppressive.
Does dew point ever exceed air temperature?
No — air can't hold more moisture than 100% saturation. Dew point equals air temperature only at 100% RH (fog, rain).
What dew point is comfortable?
Below 55°F: comfortable. 55–65°F: noticeable but tolerable. 65–70°F: humid. 70–75°F: very humid. Above 75°F: extremely uncomfortable; tropical conditions.