Pressure washer brands compared: the max PSI number is not the machine

Pressure washers are sold on one number and used on a different one. The number on the box is max PSI: the highest pressure the pump reaches for an instant, with the trigger barely open and almost no water moving. The number that cleans your driveway is the rated pressure the machine holds while it is also moving its rated flow. On one of the machines below those two figures are 2100 and 1800. On another the maker publishes only the lower one. On the third they are the same number, because that brand submits its claims to an outside body. This page ranks three brands on which of those numbers they will actually print.

The short answer

The four numbers, and why most brands publish two

A pressure washer pump trades pressure against flow. Push the pressure up and the flow falls; open the flow up and the pressure drops. That is a curve, not a pair of independent dials, which means a machine has four interesting figures and not two.

• Max PSI. Peak pressure, at minimal flow. A real measurement of a condition you never clean in.
• Max GPM. Peak flow, at minimal pressure. Also real, also not a working state. Westinghouse is explicit that its figure is taken "at lowest pressure".
• Rated PSI. The pressure held while the machine delivers its rated flow. This is the washing number.
• Rated GPM. The flow delivered at rated pressure. This is what carries the dirt away and what a surface cleaner attachment runs on.

Publish only the two max figures and you describe a machine that cannot exist, because the two maxima occur at opposite ends of the curve. Publish only the two rated figures and you are honest but look weaker than a competitor quoting maxima. That tension is the whole reason this category's numbers are such a mess, and it is why a brand that prints all four is worth noticing.

What each brand publishes

The arithmetic: what the max numbers are worth

Cleaning units — PSI multiplied by GPM — are the standard way to reduce a washer to one figure, and they are only meaningful if you multiply the rated numbers. Westinghouse is the one brand here that gives us both sets, so it is the one case where we can measure the size of the exaggeration the whole category runs on.

1. Westinghouse — the clearest published numbers

Westinghouse's spec table for the ePX3100s has four rows where every other maker has two: Max PSI 2100, Max GPM 1.76, Rated PSI 1800, Rated GPM 1.2. Then, in its own description, it writes that the machine "delivers 2100 max PSI and 1.76 max GPM at lowest pressure, with rated performance of 1800 PSI and 1.2 GPM". That clause — at lowest pressure — is the single most useful sentence published by anyone in this category, because it tells you the two headline numbers belong to different moments.

The rest of the sheet is the deepest here too: axial cam pump, Total Stop System, M22 quick-connect, a 25/64 in hose bore, a 13 A motor, 20 ft of hose, a 35 ft GFCI cord, a UPC, and both warranty terms stated separately (3-year residential, 1-year commercial). At 10 lb and 13 x 9.75 x 8 in it is a machine that lives on a shelf.

Two honest marks against it. Its rated output is the lowest of the three, so the transparency is not power. And its own page cannot agree on what it weighs: the spec table says Unit Weight 10 lbs and the body copy says a "10 pound design", while the feature bullets say "only 13.5 pounds". It also names no certifying body, so "rated" here is Westinghouse's word rather than a third party's. Three nozzles and a plastic wand, against Sun Joe's five nozzles and stainless lance.

#ad Check the Westinghouse ePX3100s Electric Pressure Washer price on Amazon — how we're funded.

2. Sun Joe — the most certified output, and a missing number

Sun Joe does something none of the others do: it puts the word Certified Rated in the product title itself, and publishes 2030 PSI and 1.2 GPM as certified rated figures in its description and its bullets. That is the highest rated output on this page — 2,436 cleaning units, 13% above the Westinghouse and 23% above the Greenworks — and it comes with the best accessory set: five quick-connect nozzles (0, 15, 25, 40 and soap), two removable 0.9 L detergent tanks, a 34 in stainless steel lance with brass fittings, a wire-reinforced 20 ft hose, a 35 ft cord, Total Stop System and a 2-year warranty with CSA listing.

Two things it does not do. It never names the certifying body on its own page — "certified rated" appears perhaps a dozen times and PWMA appears nowhere, so to find out who certified it you have to read the retail listing, which says "2030 PSI PWMA Rated". And its own page omits the max figure entirely: the retail listing leads with 2500 Max PSI, a number that appears nowhere on shopjoe.com. That is the opposite failure from Westinghouse's — here the maker is conservative and the listing is loud — but it still leaves a buyer comparing a 2500 on one box against a 2100 on another when the honest comparison is 2030 against 1800.

#ad Check the Sun Joe SPX3000 Electric Pressure Washer price on Amazon — how we're funded.

3. Greenworks — the only brand that names a body

Greenworks sidesteps the max-versus-rated problem by not having one. Its GPW1800 spec table lists Max PSI 1800 and Max GPM 1.1, and its key features describe the same 1800 PSI and 1.1 GPM as "rated cleaning power". Max and rated are the same pair of numbers. And the row that matters sits two lines below: Certifications: PWMA. That is the only third-party performance standard cited by name by any brand on this page, and it is what lets a single pair of figures stand without a caveat.

It is also the gentlest machine here at 1,980 cleaning units, which on this site is a recommendation rather than a complaint: 1800 PSI is the right pressure for vinyl siding and painted wood, as our pressure washers for siding page works through. It ships the longest hose of the three at 25 ft, five nozzles including a turbo, a 35 ft inline-GFCI cord and 8 in wheels on an open frame.

The mark against it is a data-integrity one, and it is small but real: the page's own title reads "1800 PSI 1.2 GPM Pressure Washer (Open Frame) PWMA Certified" while the product name, the key features and both spec tables all say 1.1 GPM. We publish 1.1, because that is the figure in the structured fields and in the certified claim, and we note the 1.2 in the title tag rather than pretending we did not see it.

#ad Check the Greenworks GPW1800 1800 PSI Corded Pressure Washer (PWMA Certified) price on Amazon — how we're funded.

Where the cordless machines sit in this

All three brands above are corded. Greenworks also publishes a 60V cordless washer at up to 3000 PSI and 2.0 GPM with a published eco mode of 2200 PSI / 1.0 GPM and up to 30 minutes of runtime — and notice that it needs an eco mode at all, which is the battery version of the same pressure-against-flow trade. Multiply its headline figures and you get 6,000 cleaning units; multiply its eco figures and you get 2,200, which is about what the corded machines on this page make continuously and without a battery to flatten.

That is a class decision rather than a brand one, and our corded versus cordless pressure washer page takes it apart properly. The short version: a corded washer holds its rated output for as long as you hold the trigger, and every machine on this page draws 13 A, which is a real constraint on the cord you feed it — see our outdoor extension cords page for the gauge arithmetic.

One brand we researched and did not rank

Kärcher belongs in a comparison like this: its K1700 is in stock, well known, and its listings say CETA certified, which would have given this page a second certification body to weigh against PWMA. We left it unranked because we could not open Kärcher's own US product page for it, and the retailer listings that do carry figures disagree with each other — 1700 PSI rated in one place against a 2125 PSI maximum in another, 18 ft of hose against 20 ft. On a page whose entire subject is which published numbers you can trust, publishing numbers we could not read at the source would be self-defeating. If Kärcher's US spec page becomes reachable, this page gets revisited.

How to read any pressure washer listing after this

1. Find the rated figures, not the max ones. If a listing gives only one PSI number and calls it "max", you do not know what the machine washes at. Look for "rated", or for a named certification.
2. Multiply the rated pair. Rated PSI x rated GPM is the only cleaning unit figure worth having. Anything computed from maxima describes a machine that does not exist.
3. Treat a named body as worth more than an adjective."Certifications: PWMA" in a spec table is checkable. "Certified rated" with no body named is the manufacturer vouching for itself.
4. Check GPM before PSI for big flat surfaces. Flow carries debris and drives a surface cleaner; our surface cleaners page shows that every attachment on the market is rated above the flow homeowner machines actually deliver.
5. Match pressure to the surface, not to your budget. 1800 PSI is correct for siding; concrete wants more. Our buying guide and nozzles guide cover which number does what.

Which brand, by what you are buying for

Verdict

On the only axis this page ranks — what a brand will put in print — Westinghouse wins outright, and the fact that it is also the cheapest machine here is the most useful thing on the page. Greenworks is the one brand whose claim a third party has checked, and the gentlest machine, which makes it the siding answer. Sun Joe makes the most certified output and has the best accessories, at about 45% more per unit of cleaning and with the body that certified it named only on the listing rather than on its own page. And the number to take away: on the one machine here where we can measure it, the figure you could compute from the marketing is 1.71 times the figure the machine makes while it is actually washing.