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 loose caked-on dirt or old paint. GPM (gallons per minute) measures water flow, which determines cleaning speed, how quickly that pressure clears debris and rinses a surface clean. Multiply PSI by GPM and you get 'cleaning units' (CU), a single number for comparing overall cleaning power across machines.
Electric Pressure Washers: Light-Duty and Low-Maintenance
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, skip the fuel and oil changes, start instantly, and are lighter to move, though the cord limits your range and they generally can't match gas models on large driveways or heavily soiled surfaces. Electric is the right call for occasional residential use where ease of use matters more than raw power.
Gas Pressure Washers: Driveways, Siding, and Bigger 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, need fuel and regular oil maintenance, and weigh more, but deliver roughly 2-3x the cleaning units of a typical electric unit. For a full driveway, a big deck, or an annual house wash, gas is the better investment despite the extra 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; and 3,300+ PSI for heavy stripping, stubborn stains, or commercial and fleet use. Test on an out-of-the-way spot first and use the widest nozzle angle (25-40 degrees) that still gets the job done; narrow zero-degree tips can gouge wood, damage soft siding, or strip paint at high PSI.
Nozzle Tips and Protecting the Surface
Most pressure washers ship with color-coded nozzle tips: red (0°) is a concentrated jet reserved for the toughest stains, 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. Start with a wider-angle tip and work down to a narrower one, not the reverse, and you'll avoid most surface damage.
Frequently asked questions
What PSI do I need to clean a concrete driveway?
Most driveways clean up at 2,900-3,300 PSI with at least 2.0 GPM. Heavily stained or oil-marked concrete may need the higher end of that range or a surface cleaner attachment.
Is more PSI always better?
No. More PSI raises the risk of gouging 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 for a small townhouse patio?
Electric is plenty and more convenient for a small patio, deck, or car-washing routine, given the shorter cleaning runs and lack of a large concrete area.
What does GPM add that PSI doesn't?
GPM governs how quickly loosened dirt and debris rinse away and how much surface area you cover per minute. Two washers with identical PSI but different GPM will clean a driveway at noticeably different speeds.