Temperature-change humidity calculator
Air holds a fixed amount of moisture, but relative humiditychanges the moment you heat or cool it. Enter the air now and a new temperature to see the new RH — and whether cooling will cause condensation.
Evidence-checked. Facts and figures on this page are verified against published standards and government sources (Magnus dew-point formula (Sonntag coefficients)). Last verified July 2026 — our methodology.
New relative humidity
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- Started at
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- Dew point (unchanged)
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- What changed
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Heating or cooling a sealed parcel of air does not add or remove any water, so its dew point stays the same. Relative humidity is the air's actual vapour pressure divided by the saturation pressure at the current temperature — and saturation pressure rises fast with warmth. Warm the air and RH falls; cool it and RH climbs until, at the dew point, it reaches 100% and condensation begins.
Why heating dries air and cooling wets it
This is why homes feel dry in winter: cold outdoor air is dragged inside and heated, which slashes its relative humidity even though no moisture left. It is also why a cold basement, a chilled window, or an air-conditioned surface sweats — warm indoor air cooling against them crosses its dew point. To turn a temperature and humidity into a dew point directly, use thedew point calculator; to check when your glass will fog, try thewindow condensation calculator. For the healthy indoor range, seeideal indoor humidity levels.