Pressure Washer Nozzle Calculator Calculate The Nozzle Size Enter flow rate: (GPM) Enter pressure: (PSI) Nozzle size = (Orifice) Calculate The Pressure From Nozzle Enter flow rate: (gpm) Enter nozzle size: (Orifice) Pressure = (psi) Calculate Flow Rate Enter nozzle size: (Orifice) Enter pressure: (psi) Flow rate = (gpm)