GPM and PSI are both equally important. It is the combination that is important and helps in making a pressure washer that renders the right power.nnPSI (Pounds per square inch) is referred to as the amount of pressure a unit can produce.nnWhile GPM (Gallons per minute) is the amount of water coming out of the unit. The Multiplication of both GPM and PSI is CU (Cleaning unit).nnLet's assume a pressure washer has a 3600PSI of pressure, and a 2.4 GPM water output capacity, it will produce 8640CU of cleaning. The higher the number, the more useful is a pressure washer.