Relative Humidity Calculator
Calculate RH (%) from temperature and dew point
How to Use This Calculator
1
Enter Air Temperature
Use °C for dry-bulb temperature.
2
Enter Dew Point
Provide dew point in °C.
3
Calculate
The result shows relative humidity in percent.
Formula
RH = 100 · exp( a·Td/(b+Td) − a·T/(b+T) )
with a = 17.625, b = 243.04 °C
Example: T=25°C, Td=16°C → RH ≈ 55%
About Relative Humidity
Relative humidity expresses how close the air is to saturation. It depends on temperature: warmer air can hold more water vapor.
Frequently Asked Questions
Why does RH drop when temperature rises?
Saturation vapor pressure increases with temperature, so the same absolute moisture yields a lower RH.
Is 100% RH always raining?
Not necessarily; 100% RH means saturation. It may produce fog or dew; rain needs cloud processes.