The term humidity is the amount of water vapour or atmospheric moisture present in gas. Relative humidity means the fraction of moisture that is present in air with respect to the maximum humidity at a particular temperature. Relative humidity is determined by taking into consideration the water vapour that is consisted in air and the quantity of relative humidity is expressed in the form of percentage. Determination of relative humidity is very important in art because, many artwork and its preservation is based on relative humidity.  Exposure of artworks made with organic material to relative humidity for a long time will lead to fungi growth.