PSI vs GPM: what each one actually does
PSI (pounds per square inch) measures water pressure, which determines cleaning force, how well the washer blasts off caked-on dirt or paint. GPM (gallons per minute) measures water flow, which determines cleaning speed, how quickly that pressure clears debris and rinses a surface. Multiply PSI x GPM to get 'cleaning units' (CU), a useful single number for comparing overall cleaning power across different machines.
Electric pressure washers: light-duty and convenient
Electric models typically run 1,300-2,000 PSI at 1.2-1.8 GPM, plenty for cars, bikes, grills, patio furniture, and small decks. They're quieter, need no fuel or oil changes, start instantly, and are lighter to maneuver, but the cord limits range and they generally can't keep pace with gas models on large driveways or heavily soiled surfaces. Electric is the right choice for occasional residential use where convenience matters more than raw power.
Gas pressure washers: driveways, siding, and heavy jobs
Gas models typically run 2,800-4,000+ PSI at 2.0-4.0 GPM, cutting cleaning time significantly on large concrete surfaces, fences, and multi-story siding. They're louder, require fuel and periodic oil maintenance, and are heavier, but deliver roughly 2-3x the cleaning units of a typical electric unit. For a full driveway, a large deck, or annual house washing, gas is usually the better investment despite the added upkeep.
Matching PSI to the surface you're cleaning
As a general guide: 1,200-1,900 PSI for cars, motorcycles, and screens; 2,000-2,800 PSI for decks, fences, and grills; 2,900-3,300 PSI for driveways, concrete, and siding; 3,300+ PSI for heavy stripping, stubborn stains, or commercial/fleet use. Always test on an inconspicuous area first and use the widest nozzle angle (25-40 degrees) that still gets the job done, since narrow zero-degree tips can etch wood, damage soft siding, or strip paint at high PSI.
Nozzle tips and surface protection
Most pressure washers ship with color-coded nozzle tips: red (0°) is a concentrated jet for the toughest stains only, yellow (15°) for stripping and heavy-duty cleaning, green (25°) for general all-purpose cleaning, white (40°) for delicate surfaces like cars and siding, and black (soap) for low-pressure detergent application. Starting with a wider-angle tip and working down to a narrower one, rather than starting narrow, is the safest way to avoid surface damage.
Frequently asked questions
What PSI pressure washer do I need to clean a concrete driveway?
Most driveways clean effectively at 2,900-3,300 PSI with at least 2.0 GPM; heavily stained or oil-marked concrete may benefit from the higher end of that range or a surface cleaner attachment.
Is a higher PSI always better?
No, higher PSI increases the risk of etching wood, stripping paint, or damaging soft siding and vehicle finishes; match PSI to the surface and use the widest effective nozzle angle rather than defaulting to maximum pressure.
Electric or gas pressure washer for a small townhouse patio?
Electric is usually sufficient and more convenient for a small patio, deck, or car-washing routine, given the shorter cleaning runs and lack of large concrete area.
What does GPM affect that PSI doesn't?
GPM controls how quickly loosened dirt and debris get rinsed away and covers more surface area per minute; two washers with identical PSI but different GPM will clean a driveway at noticeably different speeds.