Does a pressure washer’s PSI characterize its effectiveness?

When comparing pressure washers, consumers tend to fixate on the PSI. But to determine a pressure washer’s true cleaning capacity, you need to factor in both PSI and GPM. If you’re unclear about what these two specs say about a unit’s cleaning ability, this article is for you.

Why are PSI and GPM important?
To effectively clean a surface, a pressure washer needs to be able to do two things: separate dirt and grime from the washing surface, and rinse it away. A unit’s ability to do the first action is partially measured by PSI; its ability to do the second action is measured by GPM.

What is PSI?
PSI stands for pounds per square inch. It refers to the intensity of the pressure with which the machine sprays. Think of PSI as the brute force of the water stream. When a pressure washer boasts a high PSI, you can count on it to lift the stickiest and most stubborn gunk. The PSI of effective commercial pressure washers ranges from about 2,000 to 3,000.

What is GPM?
GPM stands for gallons per minute. It refers to the flow rate or the volume of water that moves through the pressure washer’s nozzle every minute. Think of GPM as rinsing power. The higher a pressure washer’s GPM, the quicker you can wash a surface clean. The GPM of effective commercial pressure washers ranges from 2.2 to 10.

Which spec is more relevant?
Now that you understand what PSI and GPM refer to, you can appreciate why both these specs are important in determining a pressure washer’s cleaning capacity. That said, very often contractors and professional cleaners pay particular attention to the GPM. They typically use powerful detergents in their pressure washers, which effectively dissolve dirt and grime in order to lift the debris from the surface more easily.

Moreover, it’s important to know that when a machine has a high PSI (in particular, in excess of 3,500), the water pressure can damage certain surfaces. If you require extra stripping power for stubborn dirt and grime, generally it’s better to use a detergent or to increase the water temperature.
Finally, note that the more pressure a machine delivers, the more physically demanding it is on the operator who has to offset the force of the water stream. Pressure washers with a high PSI can be more difficult and taxing to use.

What are cleaning units?
The cleaning unit (CU) is the figure obtained when you multiply the PSI by the GPM. This spec gives you a fairly good idea of the cleaning power of a specific pressure washer. However, this number doesn’t tell the whole story. Two pressure washers can have the same CU without having the same cleaning chops.

For example, say one pressure washer has a PSI of 3,000 and a GPM of 2.0, and a second pressure washer has a PSI of 2,000 and a GPM of 3.0.

Both have a CU of 6,000, but the second pressure washer with the higher GPM will deliver the faster clean, as it can rinse away dirt more efficiently.

Man washing floor with pressure washer

Get the best pressure washer for your cleaning needs
For a pressure washer that cleans the grimiest of surfaces in the shortest amount of time, choose Hotsy. With over 100 models available, Hotsy Water Blast has the right portable or stationary pressure washer to meet your cleaning needs. We have 10 convenient locations across Western Canada, including Calgary, Edmonton and Vancouver. To learn more about our products and services, contact us today!