Given below NPSHA formula to calculate Net Positive Suction Head Available. It is the absolute pressure at the suction port of the pump. Low pressure which produces at the suction side of a pump may cause the fluid to start boiling due to cavitation. Net Positive Suction Head Available formula is defined as (P_a-P_v+P_n)/ρ. Add the atmospheric pressure and gage pressure, then subtract the obtained value with vapor pressure. Finally, divide the obtained result with density to get NPSH available.