Pressure Washer Size Calculator
Not sure what size pressure washer do I need? Pick the cleaning job below and this free calculator instantly recommends the right PSI range, the GPM (flow) you need, and the total cleaning power (cleaning units) for the job — plus whether an electric or gas model makes sense. No signup, results update as you change the inputs.
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Used for a rough cleaning-time estimate.
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How to use this calculator
Start by choosing the cleaning job from the dropdown — a car, a wooden deck, house siding, a concrete driveway, or heavy equipment. The calculator immediately shows the PSI range recommended for that job, the typical GPM (gallons per minute) for that class of washer, and the resulting cleaning units, which tell you the total cleaning power.
If you know the size of the area you need to clean, enter the square footage and you will get a rough time estimate. Cleaning rate varies with dirt, experience, and equipment, so treat this as a ballpark figure for planning your afternoon, not a guarantee.
Finally, check the duty-class and electric-vs-gas note. Light jobs are fine with an inexpensive electric model, while concrete and heavy machinery almost always justify a gas-powered unit.
How it works
The calculator looks up the recommended pressure range for your job, then multiplies the midpoint of that range by the typical GPM for that class of washer to get cleaning units (CU) = PSI × GPM. Cleaning units are the fairest single number for comparing washers, because a high-PSI machine with very low flow can clean slower than a lower-PSI machine with high flow.
| Cleaning job | Recommended PSI | Typical GPM | Cleaning units |
|---|---|---|---|
| Car | 1,200–1,900 | 1.3 | 2,015 |
| Deck & patio (wood) | 2,000–2,800 | 1.8 | 4,320 |
| House siding | 2,000–2,500 (wide nozzle; soft wash is safer) | 2.0 | 4,500 |
| Driveway & concrete | 2,800–4,000 | 2.5 | 8,500 |
| Heavy equipment & machinery | 3,000–4,500 | 3.0 | 11,250 |
Warning: more PSI is not always better. Too much pressure gouges soft wood, strips deck stain, cracks vinyl siding, and forces water behind walls. Stay within the recommended range, start with a wide 25- or 40-degree nozzle held at least 12 inches away, and test on a hidden spot first. Nozzle choice matters as much as the machine — a narrow 0-degree tip at 3,000 PSI can cut skin and destroy wood instantly.
Frequently asked questions
Is 2,000 PSI enough to clean a deck?
Yes, 2,000 PSI is enough for most wooden decks and patios, and it is the recommended minimum for deck cleaning (2,000-2,800 PSI). Keep the nozzle 8-12 inches from the surface and use a 25- or 40-degree fan tip so you don't gouge the wood.
What PSI will damage siding?
Pressures above about 2,500 PSI can crack vinyl siding, chip paint, or force water behind the siding. Stay within 2,000-2,500 PSI, use a wide 25- or 40-degree nozzle held at least 12 inches away, and consider a soft-wash setup (low pressure plus detergent) instead of raw pressure.
Should I buy an electric or gas pressure washer?
Electric washers (up to about 2,000 PSI) are quieter, cheaper, and fine for cars, decks, and siding. Gas washers (2,800-4,500 PSI) deliver the higher pressure and flow needed for driveways, concrete, and heavy equipment, but they cost more and need more maintenance.
What GPM do I need in a pressure washer?
GPM (gallons per minute) controls how fast you rinse dirt away: about 1.3 for cars, 1.8-2.0 for decks and siding, and 2.5-3.0 for concrete and heavy equipment. More GPM means faster cleaning even at the same PSI, which is why cleaning units (PSI x GPM) is a better measure of total cleaning power than PSI alone.