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How It Works
Relative humidity (RH) is the ratio of actual water vapor in the air to the maximum it could hold at that temperature, expressed as a percentage. This calculator supports two approaches: the vapor-pressure ratio (RH = AVP/SVP × 100) and the Magnus-formula dewpoint method, which relates temperature, dewpoint, and RH.
Example Problem
The actual vapor pressure is 12 mbar and the saturated vapor pressure is 20 mbar. What is the RH?
- RH = (12 / 20) × 100 = 60%
At 60% RH, the air holds 60% of the maximum moisture it could carry at that temperature.
Frequently Asked Questions
What is a comfortable indoor humidity level?
Most people find 30–50% RH comfortable. Below 30% can dry out skin and mucous membranes; above 60% encourages mold growth and dust mites.
What is the difference between dewpoint and relative humidity?
Dewpoint is the temperature at which the air becomes fully saturated and condensation begins. RH expresses how close the air currently is to that saturation point as a percentage. A dewpoint of 20°C with an air temperature of 25°C gives about 73% RH.
Why does relative humidity change throughout the day?
RH rises as temperature drops (the air’s capacity decreases) and falls as temperature climbs. That is why mornings often feel damp and afternoons feel dry even though the actual moisture content may not change much.
Related Calculators
- Cloud Base Calculator — estimate cloud ceiling from temperature and dewpoint spread.
- Lightning Distance Calculator — estimate storm distance from flash-to-thunder time.
- Heat Index Calculator — find the apparent temperature from humidity and air temperature.
- Water Vapor Pressure Calculator — compute saturation vapor pressure at a given temperature.
- Wind Chill Calculator — estimate the wind chill factor for cold-weather conditions.