PSI versus GPM
PSI describes water pressure. GPM describes water flow. Higher pressure can break stubborn material loose, while more flow helps move dirt away and cover area faster. Manufacturers may also describe cleaning power as PSI multiplied by GPM.
Cars, siding and delicate work
More pressure is not automatically better. Paint, trim, screens, wood and vehicle finishes can be damaged by excessive pressure or an aggressive nozzle used too close. Start with a wider spray pattern and greater distance, then increase cleaning intensity only as needed.
Driveways and concrete
Concrete is where stronger machines and higher flow become useful, particularly on larger surfaces. A surface-cleaner attachment can also make flatwork faster and more even than cleaning an entire driveway with a narrow wand pattern.
Electric or gas?
Electric machines tend to be convenient for lighter residential jobs and require less engine maintenance. Gas machines typically make sense when you need more output, longer sessions or frequent concrete and property cleaning. Consider hose length, pump quality, nozzle selection and storage along with headline PSI.
Bottom line
Buy for your toughest regular job, not the biggest PSI number you can find. For mixed home use, controllability and adequate GPM are often more useful than extreme pressure.