SSC CHSL Model Paper 1

The amount of water vapour in the air at any given time is usually less than that required to saturate the air. The relative humidity is the percent of saturation 89. humidity, generally calculated in relation to saturated vapour density.
Relative Humidity = $\frac{\mathrm{actual}\mathrm{vapor}\mathrm{density}}{\mathrm{saturation}\mathrm{vapor}\mathrm{density}}\times 100\%$