🌫️ Relative Humidity Calculator
Calculate relative humidity from air temperature and dew point using the Magnus approximation for saturation vapor pressure.
What relative humidity measures
Relative humidity is the amount of water vapor currently in the air compared to the maximum amount the air could hold at that temperature, expressed as a percentage. It rises as air cools toward its dew point and reaches 100% exactly at the dew point.
The formula
This calculator uses the Magnus approximation for saturation vapor pressure: RH = 100 × exp(a×Td/(b+Td)) / exp(a×T/(b+T)), where T is air temperature, Td is dew point (both in Celsius), and a = 17.625, b = 243.04 are standard Magnus constants. If you enter Fahrenheit, values are converted to Celsius internally before the calculation.
This approximation is accurate for typical atmospheric temperatures and is widely used in meteorology. This tool is for general educational and planning purposes, not official weather forecasting.