Introduction & principle
RH=100×es(Td)/es(T), using the Magnus approximation es(t)=6.112 exp(17.62t/(243.12+t)) hPa over liquid water. Air −45–60°C; dew point −80°C up to air temperature. Frost point over ice differs.
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Meteorological Calculation
Dew Point to Relative Humidity
Derive RH from simultaneous air temperature and dew point.
Use this tool
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Worked example
20°C air and 10°C dew point yield about 52.56% RH. Equal temperatures yield 100%.
Detailed usage guide
- 1Enter air temperature and dew point in °C from the same observation.
- 2Read RH and the temperature–dew point spread.
- 3Treat a dew point above air temperature as an input problem; compare subzero readings with the correct ice/water convention.
Common problems & FAQ
How does this differ from the existing humidity calculator?
The existing calculator takes RH and derives dew point; this one takes dew point and derives RH. Both assume saturation over liquid water, not ice.
Methods & references
Method reviewed November 4, 2026. These tools support learning and recording, not safety-critical decisions.
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