PSI (Pounds per Square Inch)
PSI is the unit of pressure used to rate pressure washers, measuring the force of water exiting the pump per square inch of surface area. Consumer pressure washers run 1,500-2,500 PSI; professional rigs typically produce 3,500-5,000 PSI; and specialty surface cleaners can spike above 8,000 PSI. Higher PSI is not always better — in fact, for most home exterior surfaces, high PSI is destructive. Vinyl siding, wood shingles, soft mortar, roof granules, and painted surfaces all fail under excessive pressure.
In depth
The right PSI for a job is dictated by the substrate, not the equipment's capability. Windows and cedar need well under 500 PSI applied through a fan tip from distance. Concrete driveways can take the full 3,500-4,000 PSI through a surface cleaner. Skill lies in controlling effective PSI at the surface by changing nozzle, distance, and angle — a 4,000 PSI machine held 4 feet away with a 40-degree tip hits the surface at closer to 500 PSI.
How this shows up on our jobs
We size our technique, nozzle, and distance for every surface, not just our rigs' rated PSI. That is how we deliver spotless concrete without damaging a single vinyl shutter.
Services where this matters
Related terms
GPM (Gallons per Minute)
GPM stands for Gallons Per Minute — the volume of water a pressure washer delivers per minute of operation. While PSI gets the headlines, GPM is what actually does the cleaning. Think of it this way: PSI is the hammer's strength; GPM is how many hammers you're swinging. Higher GPM means more water flowing across the surface, which means faster dirt removal, better rinsing of detergents, and shorter job times.
Pressure vs. Volume
Pressure (PSI) and volume (GPM) are the two fundamental outputs of a pressure washer, and understanding the tradeoff between them is the single biggest step an amateur can take toward professional-level results. Pressure is the force of water hitting a single point; volume is the amount of water moving across a surface over time. A high-PSI, low-GPM machine cleans a tiny spot aggressively — great for lifting paint, terrible for washing a driveway. A moderate-PSI, high-GPM machine cleans broadly and gently — great for siding, wood, and most large surfaces.
Surface Cleaner
A surface cleaner is a circular attachment — typically 16, 20, or 24 inches in diameter — that replaces the wand on a pressure washer for cleaning flat horizontal surfaces. Inside the housing, two or four high-pressure nozzles spin on a swivel bar, blasting the surface at a consistent angle and distance while a skirt contains the spray. The result: an even, streak-free clean across a driveway, patio, or sidewalk in a fraction of the time a wand would take — and without the wand-streak "zebra stripes" that plague amateurs.
Soft Wash
Soft washing is a low-pressure exterior cleaning method that uses biodegradable detergents and a controlled bleach solution to kill the algae, mold, mildew, and bacteria that cause staining — rather than scouring them off with brute force. A soft wash rig delivers cleaning fluid at roughly 60-200 PSI, comparable to a strong garden hose, which is safe on siding, shingles, painted surfaces, screens, and caulking. The chemistry does the work: the solution dwells on the surface, breaks down the organic growth at the cell level, and is then rinsed clean with fresh water.
Soap Distance
Soap distance is the maximum height or horizontal reach at which a pressure-washer rig can project cleaning solution through a low-pressure soap nozzle. It is a direct function of GPM, pump pressure, hose diameter, and nozzle orifice size — and it is the single best real-world benchmark for whether a rig can wash a two- or three-story home from the ground without ladders. A consumer pressure washer can project soap maybe 8-10 feet. A professional 5.5 GPM rig projects 20-25 feet. An 8 GPM commercial rig projects 35-40 feet with the right wand and tip.