Pressure Washer Nozzle Size Calculator

Washer preset:

Start with the closest washer or attachment, then edit the flow and pressure from your pump label.

Spec units:

Switch between US pump specs and metric washer manuals without changing the stored setup.

Pump flow:

Enter total pump flow before it is split across surface-cleaner or spray-bar nozzles.

Target working pressure:

Use the intended cleaning pressure, not a closed-trigger spike or pump marketing maximum.

Nozzles sharing flow:

The calculator sizes each nozzle from the per-tip flow.

tips

Spray angle:

Pick the tip pattern you plan to buy; the same orifice size applies across normal fan angles.

Stocked-size choice:

Use nearest for normal matching, larger for gentler pressure, or smaller only when the system is rated for it.

Check inputs

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Lowest component rating:

The pressure check warns when a rounded-down or undersized tip could exceed this rating.

Pressure tolerance: +/- {{ pressure_tolerance_percent }}%

A tighter tolerance flags more rounded sizes as high or low pressure.

Wear allowance: {{ wear_allowance_percent }}%

Leave at 0 for a new tip; raise it to see how wear can quietly lower working pressure.

Measured bucket-test flow:

Optional; the formula continues to use the pump flow field above unless you edit it.

Metric	Value	Use	Copy
{{ row.metric }}	{{ row.value }}	{{ row.use }}

Pattern	Typical code	Use	Copy
{{ row.pattern }}	{{ row.code }}	{{ row.use }}

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Pressure washer nozzle size is the small opening that makes pump flow turn into working pressure. A pressure washer pump is trying to move a certain amount of water each minute. The nozzle decides how much resistance that flow meets at the wand, surface-cleaner bar, or rotary tip.

The nozzle number used on pressure-washer charts is a flow reference. A size 4 nozzle is the opening that passes about 4 GPM at 4000 PSI, a size 5 passes about 5 GPM at 4000 PSI, and so on. At lower pressure the same opening passes less flow. At the same pump flow, a smaller opening raises pressure and a larger opening lowers pressure.

Pressure washer pump flow through hose, wand, nozzle orifice, and spray angle

Spray angle is a different choice from orifice size. Red, yellow, green, white, and black tips spread the water into different patterns, but the pressure and flow match still depends on the orifice number. Surface cleaners add another wrinkle because the pump flow is split across two or more nozzles, so each nozzle is sized from per-tip flow rather than total pump flow.

Nozzle selection also affects safety. A tip that is too small can push pressure above the washer's target and possibly above the lowest-rated component in the pressure path. A worn or oversized tip usually lowers pressure and cleaning impact. A sizing estimate should be checked against the pump manual, component ratings, a pressure gauge, and real bucket-test flow when accuracy matters.

How to Use This Tool:

Start from the washer's rated or measured flow and the working pressure you want with the trigger open.

Choose a Washer preset if one matches the setup. Presets fill common flow, pressure, nozzle count, spray angle, stocked-size strategy, and component rating values.
Set Spec units to US specs (GPM + PSI) or Metric specs (L/min + bar). Metric entries are converted to the standard GPM and PSI formula.
Enter Pump flow and Target working pressure. Use pump output or bucket-test flow, not faucet supply flow.
Set Nozzles sharing flow. Use 1 for a wand tip and 2 or more for surface cleaners or spray bars with identical nozzles.
Choose Spray angle and Stocked-size choice. Nearest is the normal chart match, larger lowers pressure, and smaller raises pressure.
Open Advanced to set the lowest component rating, acceptable pressure tolerance, wear allowance, and optional measured bucket-test flow.
Review Nozzle Match for the exact orifice, recommended stocked orifice, predicted pressure, component-rating check, worn-tip estimate, cleaning units, and bucket-test comparison. Use Tip Code Guide and Pressure Map for buying and pressure tradeoff checks.

Interpreting Results:

Recommended stocked orifice is the buying number. The tip code combines the selected spray-angle prefix with that orifice number, so a 25 degree pattern with a 4.0 orifice becomes a code such as 25040. Turbo tips show the same orifice number with a rotary label.

Predicted pressure with stocked tip is the main safety and performance check. On target means the predicted pressure is inside the selected tolerance band. High pressure means the rounded orifice is smaller than ideal, Low pressure means it is larger than ideal, and Over rating means the pressure is above the entered lowest component rating.

A matching tip code is not proof that the machine is safe to run. Verify the lowest pressure rating across pump, hose, gun, lance, couplers, and nozzle holder. If the bucket-test flow differs from the entered pump flow, redo the sizing with measured flow before buying surface-cleaner or spray-bar tips.

Technical Details:

Pressure-washer nozzle numbers are based on the hydraulic nozzle capacity convention at 4000 PSI. That convention lets a chart or formula translate between pump flow, target pressure, and a unitless orifice size. The tool divides total pump flow by nozzle count first, then sizes each identical nozzle from that per-nozzle flow.

The inverse pressure check is just as important as the size calculation. Once a stocked orifice is selected, pressure is recomputed from the selected size. This catches the common chart-rounding tradeoff: choosing the next smaller stocked tip raises pressure, and choosing the next larger stocked tip lowers pressure. Wear allowance estimates what happens when the opening grows larger over time.

Formula Core:

The equations normalize to GPM and PSI even when metric display units are selected.

\begin{array}{lcl} Per-nozzle GPM & = & \frac{pump GPM}{nozzle count} \\ Exact orifice & = & per-nozzle GPM \times \sqrt{\frac{4000}{target PSI}} \\ Predicted PSI & = & 4000 \times {(\frac{per-nozzle GPM}{stocked orifice})}^{2} \\ Worn orifice & = & stocked orifice \times (1 + \frac{wear percent}{100}) \end{array}

Pressure washer spray angle prefixes
Pattern	Prefix	Common color	Typical use
0 deg pencil jet	`00`	Red	Concentrated impact for careful spot work.
15 deg chisel fan	`15`	Yellow	Strong cleaning on concrete and hard surfaces.
25 deg general fan	`25`	Green	General washing and surface-cleaner bars.
40 deg wide fan	`40`	White	Vehicles, siding, decks, and lower-impact rinsing.
65 deg soap pattern	`65`	Black	Low-pressure chemical application when the injector requires it.
Turbo or rotary	`Turbo`	Rotary	Rotating impact nozzle matched by the same orifice number.

Pressure washer stocked-tip status rules
Status	Boundary	Meaning
Over rating	`Predicted PSI > component rating PSI`	The setup exceeds the lowest entered pressure rating.
High pressure	`Predicted PSI > target PSI + tolerance`	The stocked size is smaller than ideal.
Low pressure	`Predicted PSI < target PSI - tolerance`	The stocked size is larger than ideal.
On target	Inside the selected pressure tolerance band.	The stocked size is close to the target pressure.

For example, 4.0 GPM through one nozzle at 4000 PSI gives an exact orifice of 4.0. The same 4.0 GPM split across two nozzles at 3000 PSI gives 2.0 GPM per tip and an exact orifice near 2.31, so nearest-stocked rounding can materially change the predicted pressure.

Accuracy Notes:

Nozzle sizing is a hydraulic estimate for water flow through standard pressure-washer tips. It is not a full equipment inspection.

Use the pump manual, nozzle chart, pressure gauge, and bucket-test flow when the job depends on an exact match.
Never exceed the lowest-rated pressure component in the system, including hose, gun, lance, couplers, quick connects, and holders.
Worn tips, clogged filters, inlet starvation, unloader settings, hose restrictions, and dirty nozzles can make real pressure differ from the estimate.
Spray impact can damage surfaces even when the orifice math is correct. Test an inconspicuous area before cleaning delicate materials.

Worked Examples:

A contractor wand at 4.0 GPM and 4000 PSI with one 25 degree tip gives an Exact calculated orifice of 4.0. The Recommended stocked orifice is a 4.0 orifice, and the Tip Code Guide shows a 25 degree code of 25040.

A dual-nozzle surface cleaner using 4.0 GPM at a 3000 PSI target splits flow into 2.0 GPM per nozzle. The exact orifice is about 2.31. Nearest stocked size may choose 2.5, which lowers predicted pressure, while a smaller stocked choice raises pressure and needs a component-rating check.

A troubleshooting case starts with pump flow entered as 0. The summary shows Check inputs, and Nozzle Match is not reliable until pump flow is greater than zero. Enter measured bucket-test flow if the machine does not match its nameplate GPM.

FAQ:

Does spray angle change nozzle size?

Spray angle changes the fan pattern and tip-code prefix. The orifice size is still calculated from pump flow, target pressure, and nozzle count.

Why does a larger orifice lower pressure?

With the same pump flow, a larger opening creates less restriction. Pressure Map shows how predicted pressure drops as stocked orifice size increases.

How do I size a surface cleaner?

Set Nozzles sharing flow to the number of identical bar nozzles. The calculator divides pump flow by that count before calculating each nozzle size.

What does over rating mean?

Over rating means the predicted stocked-tip pressure is above the entered Lowest component rating. Use a larger orifice, lower the target pressure, or verify the equipment rating before running the setup.

Glossary:

GPM: Gallons per minute, the pump water-flow rate used in the nozzle-size formula.
PSI: Pounds per square inch, the working pressure target or predicted pressure.
Orifice: The nozzle opening size, expressed as the pressure-washer nozzle number.
Stocked orifice: A standard nozzle size chosen near the exact calculated size.
Component rating: The lowest pressure rating of parts in the pressure path, used as a safety check.

References:

General Pump Nozzle Chart, General Pump, 2021.
Pressure Washer System Service Manual, General Pump.
Optimizing Your Spray System, Spraying Systems Co.