PSI

PSI stands for pounds per square inch and is the standard unit for measuring pressure in tires, compressor tanks, and pressure washer output. It shows up on tire sidewalls as a maximum rating, on a door jamb sticker as a recommended cold inflation pressure, and on compressor and pressure washer specs as an operating or maximum output rating.

For tires, the number on the sidewall is a maximum, not a target, while the correct everyday pressure is the one listed on the door jamb sticker, which can be lower than the sidewall maximum. Underinflated tires wear unevenly and can overheat, while overinflated tires ride harshly and reduce the contact patch touching the road, so checking PSI regularly with a gauge matters more than most drivers assume.

For compressors and pressure washers, higher PSI ratings generally mean more force behind the air or water, but PSI alone does not tell the whole story. A compressor also needs enough CFM to sustain that pressure under real tool use, and a pressure washer needs enough flow to actually clear grime rather than just blast a thin, high-pressure stream that struggles to cover a surface.