Dew Point & Humidity Calculator
The dew point is the temperature to which air must cool for water vapor to condense — a far better measure of how humid the air actually feels than relative humidity, because relative humidity changes as the air warms and cools while the dew point stays steady for a given amount of moisture. This calculator uses the Magnus-Tetens approximation to derive the dew point from a temperature and relative-humidity reading, and also reports absolute humidity in grams of water per cubic metre. A comfort rating maps the dew point onto the usual meteorological scale, from dry below 10 °C to oppressive above 24 °C. Switch between Celsius and Fahrenheit at any time.
Dew point
16.7 °C
62.1 °F
Comfort
Getting sticky
Absolute humidity
13.82 g/m³
Dew point uses the Magnus formula (a = 17.625, b = 243.04 °C). It is the temperature at which the air would reach 100% humidity and dew forms.
How to use
- Pick Celsius or Fahrenheit.
- Enter the air temperature and the relative humidity (1-100%).
- Read the dew point, absolute humidity and a plain-language comfort rating.
Frequently asked questions
- Why is dew point better than relative humidity?
- Relative humidity is relative to temperature, so 50% at 30 °C holds far more moisture than 50% at 10 °C. Dew point is an absolute measure — a dew point above ~16 °C feels muggy regardless of the air temperature.
- What dew point feels comfortable?
- Below about 13 °C feels pleasant and dry. 16-18 °C starts to feel sticky, 18-21 °C is uncomfortable, and above 24 °C is oppressive and hard to cool off in.
- What formula does this use?
- The Magnus-Tetens approximation with coefficients a = 17.625 and b = 243.04 °C, accurate to within a few tenths of a degree over normal weather ranges.
- What is absolute humidity?
- The actual mass of water vapor in a given volume of air, in grams per cubic metre. Unlike relative humidity it does not depend on temperature, so it is useful for ventilation and condensation calculations.
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