Yard Tools
PSI, GPM and cleaning units: how to choose a pressure washer
Pressure lifts the dirt, flow carries it away. Multiply them and you get the number that actually ranks these machines.
Affiliate disclosure: we earn a commission if you buy through our links, at no extra cost to you. It never changes which product we rank first — here is how we're funded.
We have not tested these units. Every spec on this page comes from the manufacturer's own documentation and is linked to it. Every computed figure is arithmetic you can redo. Prices are checked daily — last verified January 1, 1970. Here is exactly how we pick.
Pressure washers are sold on PSI alone, which is like buying a car on redline RPM. The industry has a better number and almost nobody puts it on the box: cleaning units, the product of pressure and flow. It takes one multiplication and it reorders the whole category.
The formula, and where it comes from
Generac's own support explainer sets it out: PSI provides the "oomph" you need to lift dirt and grime while GPM supplies the water to wash it away, and multiplying the two gives cleaning power. Its worked example compares a garden hose at 50 PSI and 5 GPM — 250 units — with a typical washer at 2500 PSI and 2.3 GPM, or 5,750.
That last line is the useful discovery. Eco mode is not a small saving, it is a different machine: it drops the Greenworks below the Sun Joe on cleaning power in exchange for roughly doubling the minutes per charge. Whether that is the right trade depends entirely on what you are washing.
Runtime is really a gallons figure
Sixty gallons is a car, a patio set and part of a fence. It is not a driveway. That is the honest scope of a cordless washer on one pack, and it is why the corded machine still exists: an outlet is a fuel line that never runs out. Check the Greenworks 60V washer on Amazon if reach matters more than duration.
Nozzles do more for cleaning than PSI does
Sun Joe publishes five quick-connect nozzles with the SPX3000: 0, 15, 25 and 40 degree, plus a soap nozzle. The number is the spray angle, and it changes the effective pressure at the surface far more than a few hundred PSI on the pump ever will — the same water through a narrower cone hits harder over a smaller area.
| Nozzle | What it is for | Caution |
|---|---|---|
| 0 degree | Concentrated spot removal | Will damage wood, paint and mortar |
| 15 degree | Hard surfaces, stubborn staining | Still aggressive on softer materials |
| 25 degree | General cleaning, most driveway work | The default for most jobs |
| 40 degree | Cars, windows, painted surfaces, siding | The gentle one |
| Soap | Detergent application at low pressure | Use with the detergent tanks |
Nozzle set as published by Sun Joe for the SPX3000. The usage guidance is standard spray-angle behaviour rather than a manufacturer recommendation, and the manual for your machine takes precedence.
Two removable 0.9 litre detergent tanks and a Total Stop System that shuts the pump off between trigger pulls round out that machine's published feature set. Check the Sun Joe SPX3000 on Amazon if your working area is within a cord of an outlet.
Cord length is the real spec on a corded machine
Sun Joe publishes a 20 ft hose and a 35 ft cord. Add those and you have a nominal 55 ft working radius from the outlet — less in practice, because the machine sits somewhere in between and cords do not run in straight lines. If the far corner of your property is 80 feet from a socket, that is a decision the spec sheet has already made for you.
Which one to buy
Buy the cordless if the job moves
6,000 cleaning units at full output, no cord, and an Eco mode published with real numbers rather than a label. Fence lines, boats, patio furniture at the end of the garden, machinery you would rather not drag to the house.
#ad Check the Greenworks 60V washer price on Amazon — how we're funded.
Buy the corded if the job is long
2,436 cleaning units, five nozzles, two detergent tanks and no runtime limit at all. A driveway is an hour of continuous work, and an hour is two cordless packs.
#ad Check the Sun Joe SPX3000 price on Amazon — how we're funded.
Cleaning units by job, and the water each one uses
Once you have the cleaning-unit figure, the useful next step is matching it to what you actually wash — and checking how much water the job needs against what a charge or a session can supply.
| Job | What matters most | Water at 2.0 GPM | Within one 30-min charge? |
|---|---|---|---|
| A car | Flow, gentle nozzle | ~20-30 gal in 10-15 min | Yes, comfortably |
| Patio furniture | Flow, 40 degree nozzle | ~20 gal in 10 min | Yes |
| A wooden deck | Low pressure, wide nozzle | ~40 gal in 20 min | Yes, just |
| A fence run | Flow and reach | ~40-60 gal in 20-30 min | Marginal |
| A driveway | Pressure and sustained flow | 100 gal+ in an hour | No -- corded territory |
Water volumes are our arithmetic on the Greenworks 60V machine's published 2.0 GPM at full output. Times are illustrative estimates of job length, not measurements.
The line falls in a predictable place: everything you can finish in half an hour suits the cordless machine, and everything measured in hours suits the corded one. That is a working-pattern decision rather than a power decision, which is why the cleaning-unit number alone does not settle it.
The supply side nobody mentions
A pressure washer cannot deliver more water than it is fed. Both machines here are fed from a garden hose, and a hose that struggles to fill a watering can will starve a 2.0 GPM pump. If your outdoor tap runs slowly, that is the constraint to fix before comparing GPM figures on a spec sheet.
Neither manufacturer publishes a minimum supply flow on the pages we cite, so we cannot tell you the threshold. What we can tell you is that a starved pump cavitates and runs hot, and that the symptom — pressure that surges and drops — is easy to blame on the machine.
What we cannot tell you
- Whether the published PSI is sustained or peak. Greenworks publishes "up to" 3000 PSI; Sun Joe publishes 2030 PSI as a max with a separately certified 1.2 GPM rated flow. Those are not identical measurement conventions.
- Eco mode runtime. Greenworks publishes the mode's output but not a separate runtime, so we do not compute one.
- Noise. Not published for either machine.
- What cleaning units leave out. Water temperature, nozzle choice and detergent all change real-world cleaning, and none of them is in the formula.
The products discussed
Specs are the manufacturer's own and linked to the page they came from. Prices come from a live daily check; where we have no verified price we say so rather than print a stale one.
Greenworks 60V 3000 PSI Cordless Pressure Washer
Greenworks · Greenworks 60V · Our score 8.2/10
#ad No verified live price right now, so we show none rather than a stale one. How we're funded.
3000 PSI and 2.0 GPM with no cord, and a published Eco mode that trades pressure for the runtime you actually need.
Published specs
| Max pressure | Up to 3000 PSI |
|---|---|
| Max flow | 2.0 GPM |
| Eco mode | 2200 PSI / 1.0 GPM |
| Runtime | Up to 30 min |
| Power | 60V battery (dual-battery kits available) |
Source: 60V 3000-PSI 2.0 GPM Electric Pressure Washer, greenworkstools.com
What the numbers favor
- Highest published pressure of the two washers here, by nearly 1000 PSI
- No cord -- works anywhere on the property
- Eco mode is published with real numbers (2200 PSI / 1.0 GPM), not just a label
- Shares the Greenworks 60V pack with the rest of that platform
What they don't
- 30 minutes of published runtime against a corded washer's unlimited
- Greenworks publishes several 60V washers at different pressures; check the SKU matches the PSI you are paying for
you wash a driveway twice a year within reach of an outlet. You would be buying 60V packs to solve a problem an extension cord already solves.
How it scores
Scores are our editorial weighting of the published specs above, not a test result. They are deliberately kept out of this page's structured data.
Sun Joe SPX3000 Electric Pressure Washer
Sun Joe · Corded 120V · Our score 7.9/10
#ad No verified live price right now, so we show none rather than a stale one. How we're funded.
2030 PSI rated with five nozzles and a 35 ft cord -- and no battery to size, because it does not have one.
Published specs
| Rated pressure | 2030 PSI (max) |
|---|---|
| Rated flow | 1.2 GPM (certified rated) |
| Motor | 13 A |
| Nozzles | 5 quick-connect (0/15/25/40/soap) |
| Detergent tanks | 2 x 0.9 L, removable |
| Hose / cord | 20 ft hose, 35 ft cord |
| Safety | Total Stop System trigger |
Source: Sun Joe SPX3000 Electric Pressure Washer, shopjoe.com
What the numbers favor
- Runs indefinitely -- no pack to discharge, no runtime figure to reconcile
- Five nozzles included rather than sold separately
- Two removable detergent tanks
- Total Stop System shuts the pump off between trigger pulls
What they don't
- Corded: a 35 ft cord plus an extension is the real working radius
- Sun Joe lists this model at both 13 A and 14.5 A across variants -- confirm the amperage on the exact SKU before buying
- Not on any battery platform, so it shares nothing with the rest of your yard kit
your working area is beyond easy reach of an outdoor outlet. A cordless washer trades runtime for the ability to walk away from the house.
How it scores
Scores are our editorial weighting of the published specs above, not a test result. They are deliberately kept out of this page's structured data.
Where to buy the tools on this page
Every link below is an Amazon affiliate link. We show no price we have not verified today, so where there is no live figure the link says "check price" and takes you to the listing to read it there.
Best cordless
Greenworks 60V 3000 PSI Cordless Pressure Washer
Greenworks · Greenworks 60V
Best corded value
Sun Joe SPX3000 Electric Pressure Washer
Sun Joe · Corded 120V
#ad As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. How we're funded.
Common questions
What are cleaning units on a pressure washer?
Is PSI or GPM more important?
How many PSI do I need for a driveway?
How long does a cordless pressure washer run?
What is Eco mode on a pressure washer?
Should I buy corded or cordless?
Sources
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