Nozzle Size Calculator
Enter your pressure washer's rated pressure and flow and the calculator gives you the nozzle size that uses all of it, rounded to the nearest stock size, with the pressure that nozzle will actually run on your machine. Running a surface cleaner? Tell it how many nozzles are on the spray bar and it splits the flow and sizes each nozzle for its share.
It works for any pressure washer, gas or electric, cold or hot, from a 2.5 GPM homeowner unit to a 10 GPM commercial rig. If you're sizing a downstream injector instead of a nozzle, use the downstream calculator. For the full explanation of nozzle numbers, spray angles and surface cleaner bars, read how to size pressure washer nozzles.
Nozzle size calculator
Enter your machine's pressure and flow and get the nozzle that puts all of it to work. Running a surface cleaner? Tell us how many nozzles are on the bar and we'll split the flow for you.
Quick reference chart
Nearest stock nozzle size for a single gun. For a surface cleaner, divide your GPM by the number of nozzles first, then read the chart.
Nozzle size = GPM × √(4000 ÷ PSI). A nozzle number is the flow that orifice passes at 4,000 PSI.
How the calculator figures your nozzle size
A pressure washer nozzle number is the flow that orifice passes at 4,000 PSI. A 4.0 nozzle flows 4 GPM at 4,000 PSI, a 5.5 flows 5.5 GPM, and so on. Your pump moves a fixed amount of water no matter what, so the nozzle is what sets the pressure: a smaller hole means more pressure, a bigger hole means less. The calculator uses the industry formula, nozzle size = GPM × √(4000 ÷ PSI), rounds to the nearest size you can actually buy, then runs the math backwards to show the pressure that stock size will produce on your machine.
Stock sizes run 1.5, 2.0, 2.5, 3.0 and so on up through 20. Most machines land close to a stock size; when yours lands between two, the calculator picks the closest and tells you how far off it is. It flags a nozzle as too small when it would push your machine more than 10% over its rated pressure, and as a little big when you'd give up more than 15%.
Reading a nozzle number
A quick-connect nozzle is stamped with four or five digits, like 2504 or 25055. The first two digits are the spray angle in degrees. The rest is the orifice size: 2504 is a 25° nozzle with a 4.0 orifice, 25055 is a 25° with a 5.5, 4003 is a 40° with a 3.0. The calculator gives you the orifice part; you pick the angle for the job.
| Color | Angle | What it's for |
|---|---|---|
| Red | 0° | A pencil jet. Cuts anything, including wood and paint. Rarely the right choice on a job. |
| Yellow | 15° | Stripping and heavy concrete prep. Aggressive; keep it off anything soft. |
| Green | 25° | The everyday nozzle for concrete, decks, equipment and most surface cleaner bars. |
| White | 40° | Rinsing and lighter surfaces like siding, windows frames and vehicles. |
| Black | Soap | A big orifice that drops pressure so a downstream injector can pull chemical. |
The angle doesn't change the flow math. A 2504 and a 4004 both flow 4 GPM at 4,000 PSI; the wider fan just spreads that water over more surface, so it hits softer.
Too small and too big
Go one size too small and the pressure climbs past the rating. The unloader bypasses the extra water back to the inlet, so you don't gain any cleaning power. What you do get is a pump running against a restriction, heat building in the bypass loop, and a gun that kicks harder than it needs to. Go too big and the pressure falls off, cleaning slows down, and you'll blame the machine for a nozzle problem.
If you're losing pressure and the machine runs fine, check the nozzle first. Orifices wear open over time, especially with hard water and chemical, and a worn 4.0 flows like a 4.5 or 5.0. A quick-connect pressure gauge at the gun tells you in ten seconds whether you're actually making rated pressure. Nozzles are cheap; replace them before you chase a pump.
Sizing nozzles for a surface cleaner
A surface cleaner splits your machine's flow across every nozzle on the spray bar. Size each nozzle for its share, not the whole machine. On an 8 GPM machine at 4,000 PSI, a 2-nozzle bar needs two 4.0 nozzles, a 3-nozzle bar needs three 3.0s, and a 4-nozzle bar needs four 2.0s. Keep every nozzle on the bar the same size and angle so the bar spins true and cleans evenly. Most surface cleaner bars run 25° nozzles.
| Machine | 2-nozzle bar | 3-nozzle bar | 4-nozzle bar |
|---|---|---|---|
| 4 GPM, 4,000 PSI | 2.0 (about 4,000 PSI) | 1.5 (about 3,160 PSI) | Too little flow per nozzle; stay with a 2-nozzle bar |
| 5.5 GPM, 3,500 PSI | 3.0 (about 3,360 PSI) | 2.0 (about 3,360 PSI) | 1.5 (about 3,360 PSI) |
| 8 GPM, 3,500 PSI | 4.5 (about 3,160 PSI) | 3.0 (about 3,160 PSI) | 2.5 (about 2,560 PSI) |
| 8 GPM, 4,000 PSI | 4.0 (about 4,000 PSI) | 3.0 (about 3,160 PSI) | 2.0 (about 4,000 PSI) |
| 10 GPM, 3,500 PSI | 5.5 (about 3,310 PSI) | 3.5 (about 3,630 PSI) | 3.0 (about 2,780 PSI) |
These are the calculator's answers for common machines. Put in your own numbers for the exact pick. A 4 GPM machine simply doesn't have enough flow to feed four nozzles at working pressure, which is why small machines belong on 2-nozzle bars like the 16" Whirl-A-Way, and why 8 GPM machines are what people run under a Whisper Wash Classic 19".
Replacement bars come with nozzles sized for a typical machine, not necessarily yours. Our Whisper Wash spray bars and Whirl-A-Way spray bars take standard 1/4" Meg nozzles, so swapping to the right size is a wrench and a couple of dollars.
Rotating turbo nozzles
Turbo nozzles are sold by machine GPM, not by orifice number, because the rotating seat is matched to the flow. Pick a Suttner ST-456 or ST-457 straight from your flow rating and skip the calculator for those.
What to buy
- 1/4" Meg nozzles for surface cleaner bars, J-Rods and quick-connect holders, in 15°, 25° and 40° angles.
- 1/4" IMEG hardened stainless nozzles when you want a tip that holds its orifice longer than brass or plain stainless.
- Colored quick-connect nozzle 5-packs in 2.5 through 4.5 for a full set of angles sized to one machine.
- Stainless J-Rod nozzle holders and the quad-coupler J-Rod so you can carry four angles on the gun and swap without stopping.
- Everything else in the Nozzles collection and the Surface Cleaners collection.
Keep reading
- How to size pressure washer nozzles: tips, guns and surface cleaners
- 4 GPM vs. 5.5 GPM vs. 8 GPM: what size pressure washer you actually need
- Pressure washing guns, J-Rods and the M5
- Downstream calculator for injector size and bleach mix by GPM
- Soft wash mix calculator for batch mixing with a 12V or gas pump
Common questions
What size nozzle do I need for my pressure washer?
Multiply your GPM by the square root of 4,000 divided by your PSI, then round to the nearest stock size. A 4 GPM, 4,000 PSI machine takes a 4.0 nozzle; a 5.5 GPM at 3,500 PSI lands on a 6.0; an 8 GPM at 3,500 PSI lands on a 9.0. The calculator at the top of this page does the math and shows the pressure each stock size will actually run.
What do the numbers on a pressure washer nozzle mean?
The first two digits are the spray angle in degrees and the rest is the orifice size. A 2504 is a 25° nozzle with a 4.0 orifice; a 25055 is a 25° with a 5.5; a 4003 is a 40° with a 3.0. The orifice number is the flow in GPM that nozzle passes at 4,000 PSI.
What happens if my nozzle is too small?
Pressure climbs past the machine's rating and the unloader bypasses the extra water, so you gain no cleaning power. The pump works against a restriction, heat builds in the bypass loop, and the gun kicks harder. Step up one size until the calculator shows you within a few percent of rated pressure.
What happens if my nozzle is too big?
Pressure drops and cleaning slows down. A nozzle one size too big on a 4,000 PSI machine typically costs you 20% to 25% of your pressure. That's fine on purpose for rinsing or delicate surfaces, but it's a common reason a machine seems weak when nothing is wrong with it.
How do I size nozzles for a surface cleaner?
Divide your machine's GPM by the number of nozzles on the spray bar, then size each nozzle for that share at your rated pressure. An 8 GPM, 4,000 PSI machine needs two 4.0 nozzles on a 2-nozzle bar, three 3.0s on a 3-nozzle bar, or four 2.0s on a 4-nozzle bar. Use the same size and angle on every nozzle; 25° is the usual angle for surface cleaner bars.
Can I run a 4-nozzle surface cleaner on a 4 GPM pressure washer?
Not well. Four nozzles only get 1 GPM each, which is below the smallest common nozzle size, so even 1.5 nozzles drop the machine to under 2,000 PSI. Small machines belong on 2-nozzle bars, and 8 GPM and up is what 4-nozzle bars are built for.
Which spray angle should I use?
15° (yellow) for stripping and heavy concrete, 25° (green) for everyday cleaning and most surface cleaner bars, 40° (white) for rinsing and softer surfaces, and the black soap nozzle for downstreaming chemical. 0° (red) cuts anything it touches and is rarely the right choice. The angle doesn't change the flow math, only how the water is spread.
Why does my pressure washer lose pressure over time?
Check the nozzle first. Orifices wear open with use, hard water and chemical, so a worn 4.0 flows like a 4.5 or 5.0 and the pressure falls with it. A quick-connect pressure gauge at the gun confirms whether you're making rated pressure. Nozzles are cheap; replace them before you chase a pump or unloader problem.
Does the calculator work for turbo nozzles?
No. Rotating turbo nozzles are sold by machine GPM because the rotating seat is matched to the flow, so pick one straight from your flow rating. The calculator is for fixed-orifice nozzles: quick-connect tips, Meg and IMEG nozzles, J-Rod nozzles and surface cleaner spray bar nozzles.
