Pressure Washer PSI vs. GPM | What's More Important?

Knowing how much power you need is key when you're shopping for the best pressure washer. It also determines if you can use an electric unit or need to upgrade to gas power. But what's more important in the pressure washer PSI vs. GPM conversation?

PSI, or pounds per square inch, is the number most people are familiar with for pressure washers. It's simply a measure of the force of impact of the water and helps you understand how well the water removes stuck debris.

As you can probably guess, the higher the PSI, the more energy the water has, so bigger is better in many cases. However, too much stress can be a bad thing. Even a moderately powerful and narrow nozzle has the potential to start spraying paint off the vehicle, ripping wood off the deck, and other types of damage. You can control the impact of the water by using the widest possible nozzle angle and still remove what you need to remove.

High Pressure Washer GPM

GPM stands for "gallons per minute" and is a measure of the flow of water delivered by a pressure washer. It is responsible for washing away the garbage you decompose. Unlike PSI, there isn't much water flow when it comes to risk of damage. The higher the GPM rating, the faster you can move it once the force has loosened it.

Pressure Washer PSI vs. GPM

In reality, it's the combination of PSI and GPM that gets the job done. The winner of the PSI vs. GPM standoff depends on the work to be performed. Do you regularly remove chewing gum from sidewalks? Are you dealing with tar stains every time you clean? You are looking for a high PSI rating. Are you doing standard household cleaning projects like siding, windows and decks? A higher GPM will help you get your work done faster.

Determining your ideal PSI (whether low or high) is a good start for most homeowners. Once you have the desired PSI, look for higher GPM numbers for greater efficiency. When you're considering two or more pressure washers with the PSI range you're looking for and you're wondering which is better, consider the cleaning unit formula. This simply multiplies the two values to give you an idea of the total cleaning potential.

Let's take as an example a couple of Simpson pressure washers in the MegaShot line.

Although the MS60921 has a higher PSI, the MSH3125-S actually has a higher cleaning unit. They're close, but in this case you can get the job done more efficiently with the lower PSI machine.

the bottom line

The best pressure washers start with a good balance of PSI and GPM due to the intentional pairing of the motor and pump. When you go up in PSI, you usually go up in GPM as well. Remember the cleaning unit formula to compare as you shop.

If you're still wondering what the best combination is, we recommend starting with a combination in the 3000 – 3500 PSI/2.0 – 2.5 GPM range. These pressure washers are good for most homeowners because they tend to work efficiently and still be affordable. Consider pairing it with a surface cleaner to clean driveways, decks, and walkways faster.

In this article, we look at the Simpson MegaShot MSH3125-S and the Simpson MegaShot MS60921, which you can pick up for around $400 at The Home Depot and Tractor Supply, respectively. Check out our MS60921 review to see how the Simpsons fared.