Dew Point Calculator
Calculate dew point temperature from air temperature and relative humidity for weather and comfort planning, free online.
Conditions
Result
Enter the temperature and humidity to see the result.
Estimates from standard published formulas for general use — not an official weather forecast or medical guidance. Calculations run entirely in your browser.
How to use this calculator
- Enter the air temperature and choose °C or °F.
- Enter the relative humidity as a percentage.
- Read the dew point and how humid/comfortable that level feels.
How it works
The Dew Point Calculator works out the temperature to which air must cool for moisture to condense, using the Magnus formula. Dew point is a better guide to how muggy it feels than relative humidity, because it does not change as the air temperature rises and falls.
It computes γ = ln(RH/100) + (a·T)/(b+T) and then the dew point Td = (b·γ)/(a−γ), with a = 17.62 and b = 243.12 °C, then converts to °F. A higher dew point means more moisture in the air and a stickier, more oppressive feel.
Worked example
20 °C at 50% humidity. At 20 °C and 50% relative humidity the dew point is about 9.3 °C — a comfortable, fairly dry level. A dew point above about 21 °C feels oppressive.
Tips
- When the dew point reaches the air temperature, relative humidity is 100% and fog or dew can form.
- High dew points raise the risk of heat stress because sweat evaporates poorly.
Frequently asked questions
What is the dew point?
The dew point is the temperature at which air becomes saturated and water vapour starts to condense into dew, fog or droplets. The closer the dew point is to the air temperature, the more humid it is.
Why is dew point better than relative humidity for comfort?
Relative humidity changes as the air warms or cools even when the actual moisture is the same. Dew point measures the moisture directly, so it is a more consistent guide to how sticky or comfortable it feels.
What dew point feels comfortable?
As a rough guide, a dew point below about 13 °C feels comfortable, 16–18 °C feels humid, and above 21 °C feels oppressive and sticky for most people.
Related tools
- Heat Index Calculator
- Wind Chill Calculator
- Absolute Humidity Calculator
- Cloud Base Height Calculator
- Frost Risk Temperature Calculator
- Air Density Calculator
Explore more in Weather & Environmental Monitoring.
Cite this tool
Zerdly. (2026). Dew Point Calculator. Retrieved from https://www.zerdly.com/tools/dew-point-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.