Pump Power Calculation Formula Specific speed of a 22 09 2018· P = Power input in kW to motor related to low efficiency pump T = Running hours per year Pump efficiency calculation example = 75% and 65% respectively P = Power input = 40 kW T = 3000 hours per year N = 18461 Units KWH So for same rating pump efficiency will increase by 10% then power saving will be 18461 KWH per year