Pressure Washer PSI vs GPM | What’s More Important?


When you’re shopping for a pressure washer, knowing how much power you need is key. It also determines if you can go with an electric unit or need to move up to gas power. But in the pressure washer PSI vs GPM conversation, what’s more important?

Pressure Washer PSI

PSI, or pounds per square inch, is the number most people are familiar with on a pressure washer. It’s simply a measure of how much force the water hits with and helps you understand its ability to remove stuck-on debris.

As you might guess, the higher the PSI, the more power the water has, so bigger is better in many cases. However, too much pressure can be a bad thing. It’s possible to start popping paint from vehicles, tearing wood away from deck boards, and other types of damage with even moderate power and a narrow nozzle. You can manage the water’s impact by using the widest nozzle angle you can that still removes what you need to.

Simpson PowerShot 3700 PSI Pressure Washer

Pressure Washer GPM

GPM stands for “gallons per minute” and is a measure of the water flow a pressure washer delivers. It’s responsible for washing away the gunk you break up. Unlike PSI, there’s no such thing as too much water flow when it comes to damage risk. The higher the GPM rating, the quicker you get things moving once the force breaks it loose.

Pressure Washer PSI vs GPM

Realistically it’s the combination of PSI and GPM that gets the job done. The winner of a PSI vs. GPM face-off would depend on the job to be performed. Are you constantly removing chewing gum from your sidewalk? Are you tackling tar stains every time you clean? You’re looking for a high PSI rating. Are you taking on standard home-cleaning projects such as siding, windows, and decks? Higher GPM will help you get the job done faster.

Pressure Washer PSI vs GPM 01

For most homeowners, identifying your ideal PSI (whether low or high) is a good start. Once you have the PSI you need, then look for higher GPM numbers to get better efficiency. When you’re considering two or more pressure washers that have the PSI range you’re looking for and you want to know which one is better, consider the Cleaning Units formula. This simply multiplies the two values together to give you an idea of the total cleaning potential.

Let’s take a look at a couple of Simpson pressure washers from the MegaShot line as an example.

MegaShot MSH3125-S MegaShot MS60921
PSI Rating3200 PSI3300 PSI
GPM Rating2.5 GPM2.4 GPM
Cleaning Units (CU)3200 x 2.5 = 8000 CU3300 x 2.4 = 7920 CU
Simpson Megashot 3300 PSI Pressure Washer Review MS60921

Even though the MS60921 has higher PSI, the MSH3125-S actually has higher cleaning units. They’re close, but comparatively, you’ll get the job done more efficiently with the machine that has lower PSI in this case.


The Bottom Line

The best pressure washers have a good balance of PSI and GPM right out of the gate thanks to an intentional pairing of the motor and pump. As you move up in PSI, you typically also move up in GPM. Keep in mind the Cleaning Units formula to compare when you’re shopping.

If you’re still wondering what the best combination is, we recommend starting with something in the 3000 – 3500 PSI/2.0 – 2.5 GPM range. These pressure washers are good for most homeowners, as they tend to work very efficiently and are still affordable. Consider pairing it with a surface cleaner to make driveway, deck, and sidewalk cleaning much faster.

For this article, we looked at the Simpson MegaShot MSH3125-S & Simpson MegaShot MS60921 and you can get them at The Home Depot and Tractor Supply respectively for around $400. Check out our MS60921 review to see how Simpson measures up.

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