Pressure Washer Size Calculator
What size pressure washer do you need? Pick your job to get the recommended PSI range, GPM, cleaning units and time estimate — or enter a machine you already own to see which jobs it fits, plus a nozzle orifice and standoff guide. 100% client-side.
What size pressure washer does your job need?
What can my pressure washer clean?
Nozzle orifice & standoff guide
What the numbers mean: PSI, GPM and cleaning units
PSI (pounds per square inch) is pressure — the cutting force that breaks dirt, mildew and stains loose from a surface. GPM (gallons per minute) is flow — the rinsing power that carries the loosened debris away. Beginners obsess over PSI, but experienced users know GPM is what finishes big jobs fast: a 2,000 PSI machine at 3 GPM (6,000 cleaning units) will wash a concrete driveway faster than a 3,500 PSI machine at 1.5 GPM (5,250 cleaning units).
Cleaning units (CU) = PSI × GPM. It is the single number that measures total cleaning power, and it is how you compare two machines honestly. Rough bands:
| Cleaning units | Class | Good for |
|---|---|---|
| 1,000–2,000 | Light residential | Cars, patio furniture, small decks |
| 2,000–5,000 | Standard residential | Decks, fences, siding, light driveways |
| 5,000–9,000 | Heavy residential | Driveways, large concrete, set-in stains |
| 9,000+ | Commercial / pro | Graffiti, fleet work, large flatwork |
Electric pressure washers top out around 2,000 PSI and 1.4 GPM — fine for cars and decks, slow for driveways. Gas machines reach 2,000–4,200+ PSI with 2.5–5 GPM, which is why they dominate concrete work.
Task → PSI / GPM reference table
Industry-standard bands this calculator uses. The "buy-at-least" point is the top of each band — cleaning units are computed from it.
| Task | PSI range | GPM | Cleaning units | Duty class |
|---|---|---|---|---|
| Car / vehicle wash | 1,200–1,900 | 1.2–1.6 | 3,040 | Light (electric) |
| Patio furniture | 1,200–1,900 | 1.2–1.6 | 3,040 | Light (electric) |
| Wood deck | 1,300–2,000 | 1.6–2.3 | 4,600 | Medium (gas) |
| Wood fence | 1,300–2,000 | 1.6–2.3 | 4,600 | Medium (gas) |
| Vinyl siding | 1,300–1,800 | 1.6–2.3 | 4,140 | Light (electric) |
| Driveway / concrete | 2,000–2,800 | 2.2–2.5 | 7,000 | Medium (gas) |
| Heavy stains / oil / graffiti | 2,500–3,600 | 2.5–4.0 | 14,400 | Heavy (gas/pro) |
| Commercial / pro work | 3,300–4,200 | 4.0–5.0 | 21,000 | Heavy (gas/pro) |
Worked example: sizing a unit for a 300 sq ft driveway
- Find the task band. Driveway / concrete → 2,000–2,800 PSI and 2.2–2.5 GPM.
- Take the buy-at-least point. 2,800 PSI × 2.5 GPM — a machine rated at least this will handle the job; a weaker one just takes longer.
- Compute cleaning units. 2,800 × 2.5 = 7,000 CU.
- Estimate time. A medium-duty unit cleans concrete at about 6 sq ft per minute: 300 ÷ 6 = 50 minutes, so plan for a typical range of 45–60 minutes.
- Size the nozzle. d = 1000 × √(2.5 ÷ (29.71 × √2,800)) ≈ 39.88 → round up to a 4.0 orifice. Use the green 25° tip at 12–18 inches of standoff.
If you already own a 2,000 PSI / 1.4 GPM electric unit (2,800 CU), the reverse tab shows it is "too strong" for a car's safe band — use a 40° nozzle and keep your distance — and "works, but slow" for the driveway: safe, but expect well over an hour for 300 sq ft.
Safety: pressure washers can injure and destroy
- Never use high PSI or a 0° (red) nozzle on softwood decks, vinyl siding, windows/glass, or car paint. Stay under ~2,200 PSI on cars and 2,000 PSI on wood.
- Standoff: start 24 inches away; never closer than 12 inches with 15°–40° nozzles. Test every new surface in a hidden spot first.
- Never aim the wand at people, pets, or electrical outlets and fixtures. Wear eye protection.
- Concrete: above ~3,500 PSI you can etch a residential slab — more pressure is not always better.
Frequently asked questions
What size pressure washer do I need for a driveway?
For a typical residential driveway, get a medium-duty unit rated 2,000–2,800 PSI and 2.2–2.5 GPM — about 7,000 cleaning units (2,800 × 2.5). That size cleans a 300 sq ft driveway in roughly 45–60 minutes. Electric washers under 2,000 PSI will work on light grime but take noticeably longer.
How much PSI do I need to clean a wood deck?
Stay in the 1,300–2,000 PSI range with a 25° or 40° nozzle, and always test in a hidden spot first. Softwoods like cedar and pine need only 500–600 PSI of effective pressure at the surface — more than that will fur the grain and leave permanent wand marks.
What is the difference between PSI and GPM?
PSI (pounds per square inch) is pressure — the cutting force that breaks dirt loose. GPM (gallons per minute) is flow — the rinsing power that carries debris away. A high-PSI, low-GPM machine cuts well but rinses slowly; a balanced machine cleans faster overall.
What are cleaning units and how are they calculated?
Cleaning units (CU) = PSI × GPM. They measure total cleaning power in one number. A 2,800 PSI machine at 2.5 GPM delivers 7,000 CU. When comparing two machines, the higher CU usually finishes the same job faster.
Is 2,000 PSI enough to clean concrete?
Yes, for light dirt and mildew on a driveway or patio. Set-in stains, oil spots, and large areas clean much faster at 2,500–3,600 PSI with 2.5–4.0 GPM. Going above 3,500 PSI on a standard residential slab risks etching the surface.
Can a pressure washer damage car paint?
Yes. Never exceed about 2,200 PSI on a car, and 1,200–1,900 PSI with a 40° nozzle held at least 12 inches away is the safe band. A 0° nozzle at close range can strip paint and dent trim in one pass.
Which nozzle should I use for each job?
Red 0° — stubborn spots on concrete only, never on wood or glass. Yellow 15° — concrete and paint stripping. Green 25° — the general-purpose workhorse for decks, siding, and driveways. White 40° — cars, windows, and delicate surfaces. Black 65° — soap application only.
How do I choose the right nozzle orifice size?
Match the orifice to your machine with d = 1000 × √(GPM ÷ (29.71 × √PSI)), then round up to the nearest standard size. Example: 2,800 PSI × 2.5 GPM → d ≈ 39.9 → a 4.0 orifice. An undersized orifice overloads the pump; an oversized one drops pressure.
How far should I hold the pressure washer nozzle?
Start 24 inches away and move closer until the surface cleans without damage — never closer than 12 inches for 15°–40° nozzles. Keep a 0° nozzle at least 12 inches from concrete and off wood, siding, and glass entirely.
Should I buy an electric or gas pressure washer?
Electric (up to ~2,000 PSI) suits cars, patio furniture, decks, and siding — quieter and cheaper. Gas (2,000–4,200+ PSI) is needed for driveways, heavy stains, and commercial work, with higher GPM that cuts cleaning time.
How long does it take to pressure wash a driveway?
A 300 sq ft driveway takes roughly 45–60 minutes with a medium-duty unit (2,800 PSI × 2.5 GPM ≈ 7,000 CU), which cleans about 6 sq ft per minute. Larger or heavily stained driveways, or smaller electric units, take proportionally longer.
Can I pressure wash vinyl siding?
Yes — use 1,300–1,800 PSI with a 25° or 40° nozzle, keep at least 12 inches of standoff, and spray downward with the siding laps so water does not get driven behind the panels. Never use a 0° nozzle on siding.
What happens if my pressure washer's GPM is too low?
The machine still cleans, but rinsing takes longer and you will need more passes — the job gets slower, not impossible. For big concrete jobs, extra GPM saves more time than extra PSI does.
Free tool by NRTechStudio