How GPM and PSI work together

The basic building blocks of power within a pressure washer are PSI (pounds per square inch) and GPM (gallons per minute). Together, they create HP, or horsepower.

The HP of a pressure washer is divided up to produce both the pressure at which the water is released (PSI) and the number of gallons that are released (GPM). For example, a 2.3 HP motor can produce 2.1 GPM at 1600 PSI or it can produce 3.0 GPM at 1100 PSI. Cleaning power is a function of both volume and pressure.

When selecting a pressure, first determine the minimum PSI you need to break the bond between the dirt and surface you are cleaning. The chart below can help you, or you may wish to contact your dealer if you need help.


Cars and SUVs 1500+ PSI
Industrial applications 1500+ PSI
Trucks, trailers, tractors, combines, silage choppers, cotton pickers 1800+ PSI
Decks, fences, siding 2000+ PSI
Livestock shelters 3000 PSI
Large surfaces such as driveways, patios 3000 PSI

After selecting a pressure washer with at least that PSI level, look at the GPM rate. The higher the GPM, the faster your cleaning job will be. That’s because once you have the necessary pressure to remove the dirt and grime, the only way to make your job faster is to increase the rate at which water is released.

You can lower the cleaning pressure capacity of a larger washer simply by changing spray nozzles or using a variable pressure wand. You can not make a smaller washer bigger. Horsepower is horsepower; a 2.3 HP motor can not pump over its capacity.

Always buy a unit big enough for your needs. Buying a unit that does not have adequate cleaning power will cost you extra clean up time and repairs in the future.

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