PSI is short for “pounds per square inch.” It is a measure of the water pressure coming out of the power washer. A typical garden hose dispenses water at about 50 PSI, and a coin-operated car wash provides about 700 PSI. A power washer, by contrast, typically dispenses water at several thousand PSI, depending upon the model.
GPM stands for “gallons per minute,” and describes how much water is flowing through the power washer.
You’ll find both of these ratings on a power washer, because they’re both important. Together, they provide your power washer’s cleaning power. PSI provides the “oomph” you need to lift dirt and grime, and GPM provides the necessary quantity of water to wash it away.
The real measure of a power washer’s cleaning power can be found by multiplying PSI by GPM. The higher the number, the greater the cleaning power. For example, a garden hose delivering water at 50 PSI and 5 GPM has a cleaning power of only 250. A power washer, however, delivering water at 2500 PSI and 2.3 GPM has a cleaning power of 5750.