Relative humidity refers to the ratio between the actual amount of water vapour in a given volume of air at a particular temperature and the total amount of water vapour needed to saturate the given volume of air at that temperature.
RELATIVE HUMIDITY= AMOUNT OF WATER VAPOUR IN THE AIR X 100%
TOTAL AMOUNT OF WATER VAPOUR NEEDED TO SATURATE AIR
How to calculate the Relative Humidity
The dry bulb thermometers measures 22 C and the wet bulb thermometer measures 21 C , the wet bulb depression is then 1 C. When the wet bulb depression is 1 C and the dry bulb thermometer is 22 C , the relative humidity is 90% . A relative humidity of 90% indicates that there is a lot of moisture in the air at that temperature.