Pressure washer PSI vs GPM comes down to two ratings the maker prints: PSI is the water pressure, and GPM is the gallons of water that flow through the machine each minute. Both are the maker’s figures, and neither one tells you how a particular job will go. I read a pump’s pressure and flow as two separate lines, because I built the drip irrigation for my orchard around them, and a washer’s spec table rewards the same habit. Below you get what each number means, the words makers print beside them, why ratings from different brands do not line up, and a way to read a table without being fooled.
Pressure Washer PSI vs GPM: What Each Rating Measures
PSI stands for pounds per square inch, and it measures pressure: how hard the water is pushed as it leaves the machine. GPM stands for gallons per minute, and it measures flow: how much water passes through the machine in a minute. A washer takes water from a garden hose, raises its pressure in a pump, and sends it through a high-pressure hose, a gun and a wand to the nozzle, so the two numbers describe one stream from two sides. My guide on how a pressure washer works walks through the pump, hose, gun and nozzle.
Both figures are ratings the maker assigns to a named model, so your manual’s rating table gives the figures for your machine. Neither one is a target for you, and neither is a result.
Key Takeaway
PSI is pressure and GPM is flow. The maker prints both, each with its own wording, and the manual’s specification table is where you read them.
When I open a spec table, I read the word printed beside each number before I read the number itself. That word tells you what the figure is: a peak, a maximum, a rating under a stated condition, or nothing at all.
What PSI Tells You on a Pressure Washer
PSI is the rating most buyers look at first, because it is the biggest number on the box. It describes pressure, so it says how hard the water is pushed. It says nothing about how much water arrives, and nothing about what your surface can take.
What the Pressure Line Describes
A pressure washer PSI figure is a maker’s rating, and the same figure can carry a different word from one brand to the next. For the SPX3000, Sun Joe prints a maximum pressure at initial discharge, per CSA internal pressure testing, and a separate rated pressure under typical load. Westinghouse prints a peak pressure and a rated maximum pressure for its ePX3500. In both manuals the word beside the figure is part of the rating.
If a table gives one pressure line and nothing else, I look for a second line in the manual before I trust the first.
What a PSI Figure Does Not Say
A PSI figure does not say what a surface can take. The manual and the care instructions of the surface or finish decide that. It also does not say how a machine of one maker stacks up against a machine of another, because each maker words and measures its own line, as the sections below show. My list of surfaces you can pressure wash goes manual by manual.
What GPM Tells You on a Pressure Washer
GPM is the flow rating, the gallons of water the machine moves in one minute. Several makers print more than one flow line for a single machine, and the manuals say what the water supply must provide.
The Flow Line and Your Water Supply
A washer draws its water from the supply you connect, so the manual also says what that supply must provide. The Sun Joe SPX3000 manual says the garden hose must have an internal diameter of at least 13 mm (1/2 in.) and be reinforced, and that the water supply must be at least equal to the washer delivery capacity. Simpson’s use and care manual calls for a source capable of providing an uninterrupted supply of clean, cold water at a minimum rate of 5 gallons per minute and 20 pounds per square inch of pressure. Westinghouse says the supply must come from a pressurized water spigot and never from a hot water source. The corded model with two detergent tanks gets its own page in my Sun Joe SPX3000 washer review.
On the drip irrigation I built, the pump head carries a 150-mesh disc filter, and I check what the supply delivers before I think about anything downstream. A washer’s inlet gets the same order of questions from me: supply first, then the machine. I do not assume a yard tap matches a washer’s flow line, so I read the manual’s water paragraph first.
One Machine, More Than One Flow Line
Pressure washer GPM figures also come with a basis word, and some manuals print several. EGO’s manual for the HPW3200, the washer in the HPW3204-2 kit, gives a maximum rated flow of 1.2 GPM with the quick connect lance and stainless steel wand connected, and 2.0 GPM with only the short pressure gun connected. Greenworks prints a maximum of 2.0 GPM and a rated 1.1 GPM for its GPW3002A on two separate lines. For EGO, then, the flow line also depends on what is attached to the gun. My EGO and Greenworks washer comparison sets the HPW3204-2 kit against the GPW3002A.
The Words Printed Beside the Numbers
Makers do not word these ratings alike. The table gives each pressure line and flow line as the manual prints it. Read it for the words, because the figures belong to different machines on different bases.
| Model and class | Pressure line as printed | Flow line as printed |
|---|---|---|
| Westinghouse WPX3400, gas | Pressure (PSI/BAR): 3400/234 | Flow Rate (GPM/LPM): 2.6/9.84 |
| Westinghouse ePX3500, corded electric | Peak Pressure 2500 PSI; Rated Max Pressure 2000 PSI | Maximum Water Flow Rate 1.76 US GPM; Rated Water Flow Rate 1.24 US GPM |
| Sun Joe SPX3000, corded electric | Max Pressure at initial discharge 2030 PSI per CSA internal pressure testing; Rated Pressure under typical load 1450 PSI | Max Flow with nozzle open 1.76 GPM at minimum pressure; Rated Flow under typical load 1.24 GPM |
| Greenworks GPW3002A, corded electric | Max. Pounds Per Square Inch Pressure 3000 PSI | Max. Gallons Per Minute 2.0 GPM; Rated Gallons Per Minute 1.1 GPM |
| Kärcher K1700 Cube, corded electric | Operating Pressure 1700psi | Max Water Volume 1.2GPM |
| EGO HPW3200 (HPW3204-2 kit), battery | Maximum Rated Pressure 3200 PSI (22 MPa) | Maximum Rated Flow (with quick connect lance and stainless steel wand connected) 1.2 GPM; (with only short pressure gun connected) 2.0 GPM |
Westinghouse’s gas manual prints neither a peak nor a rated word, while its electric manual prints both. Sun Joe words each line by test condition. Greenworks pairs a maximum pressure with a maximum and a rated flow, Kärcher’s manual calls its pressure an operating pressure and its flow a maximum, and EGO calls both figures maximum rated. Each line is a maker’s rating, not a result, and no row ranks above another. My Karcher K1700 Cube washer review looks at the foot-pedal model on its own.
Peak, Maximum, Rated and Operating
Where a maker defines its words, as Sun Joe does, the definition sits in the line itself: the maximum is the pressure at initial discharge per CSA internal pressure testing, and the rated figure is the pressure under typical load. Westinghouse and Greenworks give the word and no definition, so keep the word with the figure whenever you write it down.
In the Westinghouse gas table, the second figure in each pair is the same rating in other units, bar for pressure and liters per minute for flow, so 234 is not a second pressure line.
Why Ratings Do Not Compare From Brand to Brand
A rating compares only when two makers measured it the same way, and the table above shows makers wording their ratings in different ways. A printed figure with no named method gives you no basis to set it beside another maker’s.
What the Two Trade Standards Say
Two published trade methods exist for rating washers, CPC 100 and the PWMA standard. Both rate pressure and flow as the average of 6 readings taken every 5 minutes, and both list a 10% tolerance for deviation. A machine certified under them has to measure at least 90% of its advertised pressure and flow.
Sun Joe ties its maximum to CSA internal pressure testing, a method it names itself, and the other lines in the table above name no method. A chart that sets the pressure and flow ratings of different brands side by side gives you columns that look alike and mean different things.
A gas figure, a corded electric figure and a battery figure each sit on their own maker’s basis, so a comparison across power types inherits the same gap. A figure I cannot trace to a stated method goes in my notes with a question mark, not in my comparison. My comparison of gas and electric pressure washers sets fuel, cord and care side by side.
How to Read the Rating Lines Before You Buy or Use a Washer
Reading a rating line takes five short steps, and none of them needs a number from this page. On a new machine, the manual’s rating table is the first page I open. My guide on using a pressure washer gives the order the manuals print, step by step.
- Find the pressure line and the flow line in the manual’s specification table, and copy each with the word printed beside it.
- Check whether the table gives more than one line for pressure, for flow or for both. Several of the manuals above print two lines for one machine.
- Read any condition attached to a line, such as initial discharge, typical load or the attachments connected.
- Read the manual’s water supply paragraph and see what the supply must provide for your model.
- Compare across brands only when documented methods and conditions match; a matching word such as maximum is not proof of that.
A worked example with the Greenworks GPW3002A line shows the idea. The manual prints a maximum pressure of 3000 PSI, a maximum flow of 2.0 GPM and a rated flow of 1.1 GPM. A reader who copies only the 2.0 onto a comparison sheet has taken the maximum line and left the rated line behind, so the sheet no longer says which flow Greenworks rates the machine at. Copy both lines with their words and the sheet stays true to the manual. I cover that corded washer in my Greenworks GPW3002A pressure washer review.
What the Two Numbers Never Tell You
PSI and GPM describe the machine. They do not describe the job, the surface or the risk, and the places that settle those are the manual and the care instructions of what you wash. My guide on what never to pressure wash lists the warnings the manuals print.
Surfaces and Finishes
Check both your washer’s manual and the care instructions of the surface or finish maker before you wash, and follow their restrictions. If they prohibit pressure washing, do not use a different nozzle or setting as a workaround. No printed rating converts into a setting for a deck, a car or siding, and this page gives none. My plant protection training taught me to read a label from the top, and a surface’s care instructions get the same treatment before anything touches it.
What the Stream Can Do Whatever the Rating Says
Read the pressure washer’s manual before you connect water or power, and follow it. Its warnings, its operator rules and its steps for your exact model come before anything in this article.
Spray Safety
Never point the spray at yourself, another person, a pet or any part of the body. Keep your hands and feet away from the nozzle and the stream. Get medical care without delay for a spray wound, even if it looks minor at first. Tell the clinician that a pressure washer caused the injury.
CDC says the strong spray from a pressure washer can cause serious wounds that might first appear minor (1). A case report of an injection injury from a washer lists infection, compartment syndrome and in some cases amputation as possible outcomes, and notes that clear treatment guidelines are missing because the injury is rare (2). In US emergency department data, pressure washers accounted for far more hand injection injuries than paint equipment (3).
A review of reported injection injuries to the upper extremity, mostly from grease and paint guns, found that the location of the injury and the injected material affected the need for amputation (4). A case series of eye injuries from pressure washers reported surgery for every patient and poor visual outcomes, with one patient lost to follow-up (5). The same warnings apply whatever PSI the label shows.
On the farm I treat any pressurized equipment the same way: the label and the manual set the limits, and I do not argue with either. Before I start such equipment, I clear people and pets out of the yard.
What to Check Before You Trust a Rating
Three things carry this page. Each rating comes with a word, and the word is part of the rating. Each maker words it in its own way, so two figures from two brands rarely sit on the same basis. The manual’s table and its water supply paragraph tell you about your machine, and a single number does not. When you are ready to shop, my list of the best pressure washer models puts gas, electric and battery machines side by side.
My own tip is a card per machine: before I buy or borrow a washer, I copy its rating lines onto a card with the printed words beside each figure and keep the card with the manual. Read the water supply paragraph next, then the safety pages. A pressure washer PSI vs GPM comparison is only as good as the words printed beside the two figures on each machine.
Frequently Asked Questions
What is the difference between PSI and GPM on a pressure washer?
The difference between PSI and GPM on a pressure washer is what each one counts: PSI counts the pressure of the water, and GPM counts the gallons that flow through the machine each minute. The maker prints both in the manual’s specification table, often with a word such as max or rated beside each. Read both lines and keep each maker’s word with its figure.
What does GPM mean on a pressure washer?
GPM on a pressure washer means gallons per minute, the amount of water the machine moves in a minute under the maker’s stated condition. Some makers print more than one flow line for one machine: EGO’s HPW3200 manual, for example, gives one flow with the quick connect lance and stainless steel wand connected and another with only the short pressure gun connected. Check which line your manual attaches to your setup.
What are cleaning units on a pressure washer?
Cleaning units on a pressure washer are a combined figure that the industry builds from the pressure and flow ratings, and some makers, Greenworks among them, print it in the specification table of their manuals. The figure carries the basis words of both ratings behind it, so it does not settle a comparison between brands. The manual’s own pressure and flow lines are the ones to read.
What is a high GPM pressure washer?
A high GPM pressure washer has no fixed definition, because none of the makers’ manuals quoted on this page sets a threshold for the word high. Makers print flow on their own bases, such as a maximum, a rated or an operating figure, so one maker’s flow line does not rank against another’s. Read the manual’s flow line for the model you are looking at, with the word printed beside it.
Does the water supply have to match the GPM of a pressure washer?
The water supply has to meet the requirement the manual states for your model, and manuals word that requirement differently. The Sun Joe SPX3000 manual says the water supply must be at least equal to the washer delivery capacity, while Simpson’s use and care manual names a source capable of at least 5 gallons per minute and 20 pounds per square inch. Read your manual’s water supply paragraph and follow it.
References
- Centers for Disease Control and Prevention. Pressure washer safety. Natural Disasters. Published May 15, 2024. Reviewed August 26, 2026. Accessed October 31, 2026.
- Funato N, Sugizaki Y, Ri Y, Ichibayashi R. High-pressure injection damage caused by a high-pressure washer. Cureus. 2024;16(1):e52498. doi:10.7759/cureus.52498
- Johnson C, Newton W, LaRochelle L, Allen J, Daly C. High-pressure injection injuries of the hand in community and industrial settings: incidence and trends. Hand (N Y). 2025;20(6):917-922. doi:10.1177/15589447231218404
- Hogan CJ, Ruland RT. High-pressure injection injuries to the upper extremity: a review of the literature. J Orthop Trauma. 2006;20(7):503-511.
- Placide J, Yang MY, Gross AW, Crowell EL. Case series: traumatic ocular lacerations secondary to pressure washers. Am J Ophthalmol Case Rep. 2022;27:101612. doi:10.1016/j.ajoc.2022.101612
Safety Note: Read your pressure washer’s manual before you connect water or power, and follow it. Never point the spray at yourself, another person, a pet or any part of the body. Keep hands and feet away from the nozzle and stream. Get medical care without delay for a spray wound, even if it looks minor at first. Tell the clinician that a pressure washer caused the injury. Wear safety glasses or goggles and closed footwear before operating the washer, plus any additional protection required by the manual and the detergent label. Follow the manual’s instructions for the trigger lock, grip, footing and recoil, and engage the trigger lock whenever you stop spraying. Use only the nozzles, accessories and detergents the manual permits, and never point any nozzle at skin, people or animals. Do not perform a task at height without instructions expressly permitting the equipment and method in the exact manual. Gas models: operate outdoors, never inside a building or a partly enclosed space. Keep the engine at least 20 feet from any window, door or vent, following CDC’s pressure washer guidance and any stricter manual requirement. Exhaust contains carbon monoxide, which cannot be seen or smelled and can kill. Opening doors or windows does not make indoor operation safe. Refuel only with the engine off and cool, following the manual. Corded models: use the manual’s specified electrical supply and GFCI protection, and test the GFCI before use according to its instructions. After an operating GFCI or breaker trip, do not reuse the washer until a qualified repair person has examined it. Where the washer has a grounding prong, connect it to a properly grounded receptacle and never remove the prong. Wear closed, rubber-soled footwear that provides some electrical insulation, plus any additional footwear required by the manual; footwear does not replace GFCI protection or the other electrical precautions. Never cut or splice cords. Use an extension cord only as the manual permits. Keep connections dry and away from runoff, standing water and the washing area, and keep spray away from electrical equipment. Battery models: use only the battery and charger the maker specifies for your exact model. Emergency first: if you notice an unusual odor, a change in color, too much heat, a change in shape, leaking or odd noises from a lithium-ion battery, stop using the washer and follow your battery manual’s emergency instructions. Otherwise, complete the applicable stop and make-safe procedure before hose, nozzle, wand or accessory work, clearing a blockage, cleaning, maintenance, refueling, checking oil, adding detergent, battery changes or charging, draining, moving, transporting, storing or leaving the washer. Follow your exact manual’s procedure and order. Release the trigger and engage its lock. Gas: switch the engine off and wait for it to stop; disconnect the spark plug wire before service as the manual directs, and let hot parts cool before refueling, storage or contact. Corded: switch off and unplug by the plug with dry hands. Battery: switch off, remove a removable battery as the manual directs and keep it away while working; for a built-in battery, follow the manual’s isolation procedure and do not open the battery compartment. Complete the manual’s water-supply shutdown and pressure-relief steps: point the gun in a safe direction at a permitted discharge location, disengage the trigger lock, squeeze the trigger as directed to relieve pressure, then reengage the lock. Do not disconnect hoses or change nozzles until pressure is relieved. If pressure cannot be relieved by the prescribed procedure, obtain service without loosening fittings. Refit and inspect parts before restoring water or power. Replace a damaged high-pressure hose; never repair or patch it. Before you wash, plan how to keep wash water, detergent and debris out of streets, storm drains, ditches and streams, and check with your city or county stormwater office about collection and disposal. Send wash water to landscaping only where local rules and the detergent label permit it and the soil can absorb it without runoff or contamination. Keep children and pets away, and never let a child use the machine. Drain and store the washer as its manual directs. For exposure to a cleaning product, follow the label’s first-aid instructions and call Poison Control at 1-800-222-1222. Call 911 for a fire or immediate danger.