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Pressure washers are appliances that are both quite simple and yet very complicated for most users. And that’s understandable. While what all pressure washers do is just jettison water out of a hose under high pressure to clean surfaces, there are still several factors many people find unclear about them.
The reason seems to be that there are multiple metrics and abbreviations around pressure washers that all correlate to each other and to the surfaces you need cleaned in different ways.
And the main offender? PSI.
So, let’s go over what PSI means, how it relates to the other pressure washer metrics, and how much PSI you need for your pressure washer.
What are PSI, GPM, and CU/CPU and how do they relate to each other?
The three main metrics you’ll need to familiarize yourself with are PSI, GPM, and CU or CPU:
- PSI – an abbreviation for pressure per square inch: PSI directly measures how strong the water jets coming out of your pressure washer are. Most pressure washers come in the 1,300 to 3,000 PSI range but some industrial models can go up to 4,000. PSI is arguably the most important metric when it comes to pressure washers as it tells you just how powerful the device is and what you can clean with it. The higher the number, the bigger the problems you can clean with it, however, the more damaging the device can be to softer surfaces.
- GPM – this is an abbreviation for gallon per minute: It measures just how much water your pressure washer uses. The lower the number, the more water-efficient the pressure washer is going to be. Of course, higher PSI pressure washers usually require more water but PSI and GPM aren’t that directly related – better pressure washers manage to generate more PSI without costing you too much GPM. So, if you want to use your device more often and you don’t want your water bill to swell too much, looking for a high PSI/low GPM device is a good idea.
- CU or CPU – these abbreviations are usually interchangeable and they mean cleaning units or cleaning pressure units. We prefer “CU” as an abbreviation over “CPU” as it can’t be confused with “Central processing unit – CPU”. What CU means in pressure washers is just the multiplication of PSI x GPM. CU is meant to be the leading metric when it comes to judging a pressure washer’s effectiveness.
From these metrics, PSI usually takes center stage. That’s because CU factors in GPM and most people just want the GPM to be lower and the PSI to be higher, without caring how much exactly the PSI x GPM of a pressure washer is.
What do we mean? Here’s an example:
- Pressure washer A has a PSI of 3,000 and a GPM of 2. Therefore, it has a CU of 6,000 (3,000 x 2).
- Pressure washer B has a PSI of 2,000 and a GPM of 3. Therefore, it has a CU of 6,000 (2,000 x 3).
Both pressure washers have the same cleaning units, however, pressure washer A is clearly the better choice as it achieves the same CU with less water.
That is, unless you actually want a lower PSI and you’re willing to pay the extra water bill for it. And why would you want that – let’s answer that next.
How much PSI is needed for the more common pressure washer tasks?
It’s intuitive to think that more PSI is always better. However, the pressure generated by pressure washers can be so high that it doesn’t just clean surfaces but it also damages them. Pressure washers in the 3,000 – 4,000 PSI range are so powerful that they are used to strip paint off of concrete. That much PSI is definitely not something you’d want to use on your car, for example.
So, lower PSI pressure washers are actually very useful in more residential situations as homeowners usually want such a device for their driveway, car, or their home’s deck and exterior walls. And to give you an idea of how much PSI the more common cleaning tasks require, here’s a quick list:
- Grafitti and paint removal: 3,500+ PSI
- Industrial equipment cleaning: 3,500+ PSI
- Asphalt driveways cleaning: 3,000+ PSI
- Exterior wall cleaning: ~3,000 PSI
- Boats and ATVs cleaning: ~2,500 PSI
- Brick wall cleaning: ~2,000 PSI
- Cedar fences: ~2,000 PSI
- Docks and decks: ~2,000 PSI
- Cars, bikes, and scooters: ~1,500 PSI
- BBQ grills: ~1,500 PSI
If you don’t want to damage the surface you’re cleaning, it’s best to use the right PSI levels for it. Fortunately, pressure washers also come with multiple nozzles and attachments that can focus or lower their PSI. So, for example, with the right nozzle, you can lower the effective pressure of a 2,500 PSI pressure washer enough to be able to clean your car without stripping its paint.
Recommended Pressure Washers
- Karcher Electric Pressure Washer – 1700 PSI
- Sun Joe SPX3000 Electric Pressure Washer – 2030 PSI
- Simpson MSH3125 MegaShot Gas Pressure Washer – 3200 PSI
What PSI to aim for with your future pressure washer?
With all those stats in mind, the question of how much PSI you need for your pressure washer seems clearer – it depends on the tasks you want to use it for. Still, it’s smart to consider not only the 2-3 cleaning tasks you have in mind but also the things you might use the pressure washer for in the future.
Additionally, once you decide what PSI range you want to go for, consider different pressure washer models in said range. Depending on whether they are gas or electric, whether they are “heavy-duty” or “light-duty”, what their GPM and CU are, and what attachments they have, a pressure washer with similar PSI can be better or worse for any given task. Read the description of each model carefully and look at what they’re recommended for.
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