Pressure Washer PSI, GPM & Nozzle Calculator

How to use this calculator

1. Enter your PSI and GPM. Both are on the machine's spec sticker or the box — e.g., "3000 PSI, 2.5 GPM." PSI is the pressure; GPM (gallons per minute) is the flow. You need both; a machine is only as good as the weaker of the two.
2. Don't know your GPM? Tap "Measure it" and run the wand (no nozzle) into a measured bucket for a timed fill. The calculator turns gallons-per-seconds into GPM and drops it into the field. Manufacturers sometimes overstate GPM, so a bucket test is the honest number.
3. Pick what you're cleaning. Fifteen surfaces — cars, wood and composite decks, vinyl and wood siding, brick, stucco, concrete, pavers, fences, gutters, furniture, windows. Each has a safe, effective PSI window baked in.
4. Read the result. Cleaning power (PSI × GPM) as the headline, with a duty class and a plain-language benchmark. The nozzle orifice size to buy. The exact spray tip for the job (with its color). And a suitability verdict — "well matched," "under-powered," or "risk of damage" — because too much pressure ruins wood, siding, and mortar faster than too little.
5. Save or share it. "Setup card PDF" builds a one-page branded reference with your numbers, the recommended tip, and the full nozzle color code — print it and tape it to the machine. "Share link" copies a URL with your exact configuration for a friend or the next job.

Why this pressure washer calculator is different

After pulling the top 10 results for "pressure washer GPM calculator," here's the gap. Almost every one is a nozzle-size-only tool from a parts retailer — you enter GPM and PSI, it spits out an orifice number, and that's it. Useful, but it answers one narrow question and then tries to sell you a $9 tip.

• They stop at the nozzle number. We start there. This tool gives you the nozzle size and the cleaning power (so you can compare two machines), and the right spray-angle tip for the specific surface, and whether your machine is safe for that surface at all. One page, the whole decision.
• Nobody warns you about too much pressure. The single most expensive mistake in pressure washing is stripping wood grain, cracking old mortar, or blasting water behind vinyl siding — all from using too much PSI on a soft surface. None of the retailer calculators flag it. This one turns red when your PSI is above the surface's damage threshold and tells you to back off or switch tips.
• Nobody shows cleaning power. Cleaning Units (PSI × GPM) is the number that actually compares machines — a 2000 PSI / 3.0 GPM washer out-cleans a 3000 PSI / 1.5 GPM one on flatwork, and CU is how you see that at a glance. Retailer nozzle calcs ignore it entirely.
• The built-in bucket test. Most people don't know their real GPM. Instead of sending you to a separate page, the GPM helper is right here — time a bucket fill and it does the math.
• No login, no ads, no cart. The retailer tools exist to sell nozzles. This one exists to get you the right answer and is free to embed on your own site.

How it works (the math behind the numbers)

Three formulas, all standard and all cited below:

Cleaning power (Cleaning Units):
  CU = PSI × GPM

Recommended nozzle orifice size:
  nozzle size = GPM × √(4000 / PSI)
  (round to the nearest available tip: 2.0, 2.5, 3.0, 3.5, 4.0 …)

Flow changes with pressure (orifice flow law, Q ∝ √P):
  GPM at a new pressure = GPM × √(new PSI / old PSI)

GPM from a timed bucket fill:
  GPM = gallons × 60 ÷ seconds

Cleaning Units (CU = PSI × GPM) is the standard cross-brand power metric. PSI provides the punch to break the bond between dirt and surface; GPM provides the water volume to flush it away. Multiply them and you get one number that ranks machines honestly — a 2,000 PSI × 3.0 GPM washer (6,000 CU) beats a 3,000 PSI × 1.5 GPM one (4,500 CU) on big flatwork, even though the second has a bigger PSI number on the box.

Nozzle sizing uses the orifice flow law: flow through a fixed opening scales with the square root of pressure (Q ∝ √P). Pressure-washer spray tips are labeled by the GPM they pass at a 4,000 PSI reference — a "4.0" tip flows 4.0 GPM at 4,000 PSI. To find the tip your machine needs, you solve for the orifice that passes your rated GPM at your rated PSI: size = GPM × √(4000 / PSI). This is the identical formula MTM Hydro, Cam Spray, Dultmeier, and the General Pump / Suttner nozzle charts all use. Example: a 3,000 PSI / 2.5 GPM machine needs 2.5 × √(4000/3000) = 2.89 → round to a 3.0 tip.

The bucket test is just a flow measurement: catch a known number of gallons, count the seconds, and GPM = gallons × 60 ÷ seconds. Five gallons in 45 seconds is 6.7 GPM at the wand's open flow. It's the most reliable way to know your true GPM when the sticker is missing or optimistic.

Every fixture in sites/diy/src/data/tools/pressure-washer-psi-calculator/fixtures.json runs in CI before each deploy. If the math drifts, the build fails.

Nozzle spray-tip color code

Every pressure washer ships with a set of quick-connect tips in a universal color code. The color is the spray angle — a wider angle spreads the same pressure over more area, so it hits softer:

• 0° red — a pinpoint blaster. Enormous force on a tiny spot; it will etch concrete and gouge wood. Rarely the right choice; skip it for almost everything.
• 15° yellow — chiseling. Caked mud, paint stripping, rust removal from metal and bare concrete. Aggressive.
• 25° green — the everyday all-rounder. Dirt, grime, and mildew off most surfaces. Start here for general cleaning.
• 40° white — gentle. Cars, vinyl siding, windows, screens, outdoor furniture. The go-to for anything you can scratch.
• 65° black — the soap tip. Low pressure by design so the pump can draw detergent; it applies suds, it doesn't clean. Spray on, let dwell, then rinse with the green or white tip.

Rule of thumb: start wide, move closer. Begin every job with the 25° (or 40° on soft surfaces) two to three feet back, and only narrow the angle or close the distance if the surface can clearly take it.

Recommended PSI by surface

This is the table the calculator's suitability verdict is built on. Treat the numbers as safe starting points, always test a hidden spot first, and keep the tip moving:

Want the reasoning behind every one of these? Jake's full write-up — how to choose the right pressure washer PSI for every job — walks through why softwood scars at 800 PSI while a driveway shrugs off 3,000.

Three worked examples

Common electric: 2,000 PSI, 1.2 GPM, washing the car

Cleaning power = 2,000 × 1.2 = 2,400 CU — light-duty, exactly right for a car. Nozzle size = 1.2 × √(4000/2000) = 1.7 → a 1.5 tip. At 2,000 PSI with the 40° white tip you're inside the safe window for automotive clearcoat; keep the tip a foot back and never use anything narrower on paint. This is textbook electric-washer territory — no need for gas.

Mid gas: 3,200 PSI, 2.5 GPM, concrete driveway

Cleaning power = 3,200 × 2.5 = 8,000 CU — heavy-duty, and concrete wants exactly this. Nozzle size = 2.5 × √(4000/3200) = 2.80 → a 3.0 tip, though for a driveway you'll actually get faster, streak-free results with a surface cleaner attachment fed by this flow. The 15°–25° tips do spot work on stains. This is the sweet spot most homeowners buy into once they have flatwork to clean.

Too much machine for the job: 3,200 PSI, 2.5 GPM, wood deck

Same 8,000-CU machine, pointed at a softwood deck. The calculator turns red: 3,200 PSI is well above the ~1,500 PSI where wood grain starts to furr and splinter. The fix isn't a different machine — it's technique. Drop to the 40° tip, keep it moving, hold it 12–18 inches back, and treat the pressure as "as little as gets it clean." A deck cleaned at 800–1,200 PSI looks restored; one blasted at 3,200 looks chewed.

What affects how accurate this is

• Rated vs. real GPM. Manufacturers sometimes quote GPM at zero back-pressure. Your real working flow is lower — the bucket test is the honest number, and it changes the nozzle size and cleaning power.
• Water supply. A pressure washer can't pump more than you feed it. A narrow, kinked, or long garden hose starves the pump and drops your effective GPM. Use a good ¾″ hose and a wide-open spigot.
• Nozzle wear. Orifices erode with use; a worn tip flows more and hits softer. If cleaning power seems to fade, the tips are usually the culprit before the pump.
• Surface condition. Old, sun-baked wood, chalky paint, and crumbling mortar tolerate far less pressure than the table assumes. When in doubt, go one tip wider and a foot farther back.
• Detergent does the work. On siding, decks, and concrete, a good cleaner that dwells for a few minutes lets you clean at lower pressure — safer for the surface and easier on you.
• Hot vs. cold water. These numbers assume a standard cold-water consumer machine. Hot-water and commercial units clean grease and oil at lower pressure than cold-water math predicts.

Frequently asked questions

How many GPM should my pressure washer be?

For general home use, 1.2–2.0 GPM (electric) covers cars, furniture, and light siding; 2.0–2.8 GPM (gas) is the sweet spot for decks, siding, and driveways; 3.0–4.0 GPM is for big flatwork and surface cleaners. Remember that GPM matters as much as PSI — it's the water volume that flushes loosened dirt away, so a higher-GPM machine cleans large areas faster even at the same pressure.

What is a good GPM for a 3,000 PSI pressure washer?

Around 2.3–2.8 GPM is the typical, well-balanced pairing for a 3,000 PSI machine — that's roughly 7,000–8,400 cleaning units, enough for driveways and two-story siding. Below ~2.0 GPM a 3,000 PSI machine feels "all punch, no rinse" and cleans large areas slowly. Enter your exact numbers above to see the cleaning power and the nozzle size.

Can you calculate GPM from PSI?

Not directly — PSI and GPM are independent specs of the machine, so you can't derive one from the other. What you can calculate is how a fixed nozzle's flow changes with pressure: GPM scales with the square root of pressure (GPM at a new pressure = GPM × √(new PSI ÷ old PSI)). To find your machine's actual GPM, read the spec sticker or run the bucket test in this tool.

What size nozzle do I need for my pressure washer?

Use nozzle size = GPM × √(4,000 ÷ PSI), rounded to the nearest available tip. A 3,000 PSI / 2.5 GPM machine needs a 3.0; a 4,000 PSI / 4.0 GPM machine needs a 4.0. That's the orifice number — separate from the spray-angle color (0/15/25/40/65°), which you pick based on the surface. The calculator gives you both.

Can I embed this calculator on my site?

Yes — copy the iframe snippet at the bottom of this page. It's free for /r/pressurewashing, /r/HomeImprovement, cleaning-service blogs, real-estate and property-management sites, and pressure-washer retailers. Required attribution is built in; no signup, no analytics attached to the embed.

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• Browse all free tools by Jake →

Recommended pressure washers & gear

Once you know the cleaning power you actually need, matching a machine is easy. Here's where Jake points people:

• Best Pressure Washers for Home Use — the overall roundup, sorted by PSI, GPM, and cleaning power for real home jobs. Start here if you're buying.
• Best Electric Pressure Washers — if your jobs land in the light-to-medium range (cars, furniture, siding, fences), electric is lighter, quieter, and maintenance-free.
• Gas vs Electric Pressure Washers — heavy flatwork and sustained GPM lean gas. This is where the real dividing line is.
• Best Garden Hoses — your GPM is capped by your supply. A proper ¾″ hose keeps the pump fed so you get the flow you paid for.
• Pressure Washer Safety Tips — the 0° tip and a ladder are how people get hurt. Read this before the first job.

Sources & methodology

• Orifice flow law (Q ∝ √P) — flow through a fixed orifice scales with the square root of pressure. Basis for both nozzle sizing and the flow-at-pressure formula. (Engineering ToolBox — Orifice, Nozzle and Venturi Flow)
• Nozzle sizing at 4,000 PSI reference — pressure-washer tips are labeled by GPM at 4,000 PSI; required size = GPM × √(4000/PSI). Matches the MTM Hydro, Cam Spray, Dultmeier, and General Pump / Suttner nozzle charts. (MTM Hydro nozzle size calculator)
• Nozzle spray-angle color code — 0° red, 15° yellow, 25° green, 40° white, 65° black soap. Universal industry standard.
• Cleaning Units (CU = PSI × GPM) — standard cross-brand pressure-washer power comparison metric used by reviewers and manufacturers.
• Recommended PSI by surface — manufacturer and trade guidance, cross-checked against DIYRated's PSI-by-surface guide.

This calculator is reviewed annually for source currency. About Jake · Last reviewed August 7, 2026.

Embed this tool on your site

Free for /r/pressurewashing, /r/HomeImprovement, cleaning-service and property-management blogs, real-estate sites, and pressure-washer retailers. Required attribution is included in the snippet. No fee, no account, no analytics attached to the embed.

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  Pressure washer calculator by
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  &middot; Reviewed by Jake Morrison, Licensed GC
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