Example: On a particular hot day, the temperature is `30°C` and the partial pressure of water vapor in the air is `21.0\ t o r r` What is the relative humidity? Solution: Water at 30°C the saturated vapor pressure is `31.8\ t o rr` relative humidity `= (21.0\ t o rr)/(31.8\ t o rr) times 100% = 66%`