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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The nozzle is the final restriction in a pressure washer system, so it has more control over working pressure than its small size suggests. A positive-displacement pump moves a certain amount of water, usually listed in gallons per minute or liters per minute. The tip opening then decides how much resistance that flow meets. Too small an opening raises pressure and stress. Too large an opening drops pressure and leaves the spray feeling weak, even when the pump itself is healthy.

Nozzle shopping can be confusing because pressure-washer tips carry two different ideas in one code. The first part describes the spray pattern, such as a red pencil jet, yellow narrow fan, green general fan, white wide fan, black soap pattern, or turbo nozzle. The orifice number describes hydraulic capacity. A 25 deg fan and a 40 deg fan can share the same orifice number, but they will put the water on the surface in very different patterns.

Working pressure: The pressure with the trigger open and water flowing through the chosen setup, not a closed-trigger spike.
Per-nozzle flow: The pump flow divided by the number of identical tips sharing it, which matters for surface cleaners and spray bars.
Stocked size: The real nozzle size available from a chart or supplier, usually chosen near the exact calculated orifice.

The common nozzle-number convention uses 4000 PSI as the reference point. A size 4.0 tip passes about 4.0 GPM at 4000 PSI. At a lower pressure, the same opening passes less water. At a higher pressure, it passes more. That square-root relationship is why two tips that look nearly identical can produce noticeably different pressure on the gauge.

Surface cleaners are a frequent source of wrong sizing because the pump flow is shared. A 4.0 GPM washer feeding a two-nozzle bar does not send 4.0 GPM through each nozzle. Each identical tip is sized around 2.0 GPM before the target pressure is applied. Buying each bar nozzle as if it carried the full pump output can make the cleaner slow, streaky, or difficult to balance.

A calculated orifice is a starting point, not a certification. Real pressure also depends on pump wear, inlet water, filters, hose length, quick-connect restriction, unloader adjustment, gauge location, clogged tips, and nozzle wear. The useful habit is to size from pump flow and intended working pressure, then check the weakest component rating and confirm the setup with a gauge or bucket test when the job matters.

How to Use This Tool:

Enter the washer setup as it will be used with the trigger open, then compare the exact hydraulic size with practical stocked tip choices.

Choose the closest Washer preset. The preset fills a realistic pump flow, target pressure, nozzle count, spray angle, stocked-size choice, and component rating. Change any value that does not match the pump plate, manual, gauge, or attachment.
Set Spec units to match the numbers you have. US entries use GPM and PSI. Metric entries use L/min and bar and are converted before the hydraulic formula is applied.
Enter Pump flow and Target working pressure. Use rated pump output or a measured value. Use the pressure you want while spraying, not the highest advertised pressure on the box.
Set Nozzles sharing flow. Use 1 for a single wand tip. Use 2, 3, or 4 when a surface cleaner or spray bar divides pump flow across identical nozzles.
Pick the Spray angle and Stocked-size choice. Nearest stocked orifice is the normal buying choice. Next larger / gentler lowers predicted pressure. Next smaller / more bite raises predicted pressure and needs a rating check.
Open Advanced for safety and troubleshooting inputs. Add the Lowest component rating, adjust Pressure tolerance, enter a Wear allowance, or compare a Measured bucket-test flow.
Read the summary and Nozzle Match first. If the summary says Check inputs, correct the flow, pressure, nozzle-count, or rating issue before using the pressure map or exported results.

Interpreting Results:

Exact calculated orifice is the mathematical opening size for the entered per-nozzle flow and target pressure. Recommended stocked orifice is the closest practical size selected from available chart increments. When those values differ, the real stocked tip will run above or below the target pressure.

Tip code combines the spray-pattern prefix with the orifice suffix. A 25 deg fan with a 4.0 orifice is commonly written as 25040. The Tip Code Guide keeps the orifice constant while showing how the prefix changes across red, yellow, green, white, black, and turbo-style choices.

On target means the stocked-tip pressure is inside the selected tolerance band.
High pressure means the chosen stocked size is smaller than ideal and may be too aggressive.
Low pressure means the chosen stocked size is larger than ideal and may clean more slowly.
Over rating means predicted pressure is higher than the entered lowest component rating.

Use the Pressure Map when choosing between neighboring stocked tips. A slightly larger tip may be the right choice for siding, vehicles, soft materials, or older components. A smaller tip can sharpen cleaning impact, but it also raises pressure and can shorten component life when the system is not rated for it.

Technical Details:

Pressure-washer nozzle sizing follows the behavior of water forced through a fixed restriction. Flow is set mainly by the pump, while pressure is produced by the resistance at the tip and by losses along the pressure path. The nozzle number is therefore a capacity rating, not a spray-angle rating.

The 4000 PSI reference makes nozzle charts reversible. If flow and desired pressure are known, the exact orifice can be solved directly. If a stocked orifice has already been chosen, the same relationship estimates the pressure that tip will produce with the entered per-nozzle flow. That second calculation is what makes rounded-size warnings useful.

Formula Core:

The calculation uses GPM and PSI internally. Metric entries are converted with 1 GPM = 3.785411784 L/min and 1 bar = 14.5037738 PSI.

\begin{array}{lcl} Per-nozzle GPM & = & \frac{pump GPM}{number of nozzles} \\ 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 nozzle formula variables
Quantity	Meaning	Important boundary
Pump flow	Total pump output before any split across nozzles.	Must be greater than zero; values above 16 GPM are flagged for chart verification.
Target pressure	Desired open-trigger working pressure.	Supported chart range is 250 to 8000 PSI.
Nozzle count	Number of identical tips sharing pump flow.	Limited to 1 through 4 for this sizing model.
Stocked orifice	The nearest, next larger, or next smaller available chart size.	Compared against stocked values from 1.5 through 50.

A 4.0 GPM washer running one nozzle at 4000 PSI gives 4.0 x sqrt(4000 / 4000), so the exact orifice is 4.0. The same pump feeding a two-nozzle surface cleaner at 3000 PSI gives 2.0 GPM per nozzle and an exact orifice near 2.31. A stocked 2.5 tip predicts about 2560 PSI, which is roughly 15% below the 3000 PSI target.

Pressure status boundary rules
Status	Boundary	Meaning
Over rating	`predicted PSI > component rating PSI`	The rounded stocked tip exceeds the weakest entered pressure rating.
High pressure	`predicted PSI > target PSI x (1 + tolerance)`	The stocked tip is smaller than the exact hydraulic size.
Low pressure	`predicted PSI < target PSI x (1 - tolerance)`	The stocked tip is larger than the exact hydraulic size.
On target	Inside the selected tolerance band.	The rounded tip is close enough for the chosen tolerance.

Pressure washer spray pattern code guide
Pattern	Prefix	Common color	Typical use
0 deg pencil jet	`00`	Red	Concentrated impact for metal, gum, and careful spot work.
15 deg chisel fan	`15`	Yellow	Strong cleaning on concrete and other hard surfaces.
25 deg general fan	`25`	Green	General-purpose washing and many 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 injector flow requires it.
Turbo or rotary	`Turbo`	Rotary	Rotating impact nozzle matched by the same orifice number.

Wear is modeled as orifice enlargement before pressure is recalculated. That matches the practical symptom of an eroded nozzle: the pump may still move the same water volume, but the larger opening creates less resistance, so measured working pressure falls. Clogging behaves in the opposite direction and should be corrected physically rather than treated as a sizing strategy.

Accuracy and Privacy Notes:

Nozzle sizing estimates hydraulic behavior for water through standard pressure-washer tips. It does not inspect the washer, verify the unloader, or certify a hose, gun, coupler, lance, or nozzle holder for the predicted pressure.

Confirm critical setups with a manufacturer chart, pressure gauge, pump manual, and measured flow check.
Never exceed the lowest pressure rating in the pressure path, even if the pump advertises a higher maximum.
Dirty filters, inlet starvation, long hoses, worn tips, clogged tips, and unloader changes can move real pressure away from the estimate.
Entries are calculated in the browser. Copied text, downloads, and JSON contain the washer setup and assumptions you entered.

Worked Examples:

Single contractor wand. A 4.0 GPM washer at a 4000 PSI target with one 25 deg fan tip lands on a 4.0 exact orifice. The stocked size is 4.0, the green fan code is 25040, and predicted pressure stays on target before wear is added.

Dual-nozzle surface cleaner. A 4.0 GPM pump at 3000 PSI splits into 2.0 GPM per tip. The exact orifice is about 2.31. The nearest stocked 2.5 tip predicts roughly 2560 PSI, while a 2.0 tip raises pressure sharply and should be checked against the component rating.

Prosumer washer replacement tip. A 2.5 GPM washer at 3100 PSI gives an exact size near 2.84 with one wand tip. A 3.0 stocked tip may read low with a tight tolerance, while a 2.5 stocked tip may be too aggressive for weaker accessories.

Troubleshooting weak pressure. If the rated pump flow looks plausible but the washer feels weak, enter a measured bucket-test flow for comparison. A large measured-flow difference points toward pump, inlet, filter, or test-condition issues before it points to a new tip.

FAQ:

Does spray angle change the orifice size?

No. Spray angle changes the fan width, impact pattern, and code prefix. Orifice size is calculated from pump flow, target pressure, and nozzle count.

Why does a larger tip lower pressure?

The same pump flow meets less restriction through a larger opening, so predicted pressure drops. Cleaning may become gentler but slower.

How do I size a surface cleaner?

Set Nozzles sharing flow to the number of identical bar nozzles. The calculation divides total pump flow by that count before sizing each tip.

What does over rating mean?

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

Can nozzle wear cause pressure loss?

Yes. A worn tip behaves like a larger orifice. The same pump flow meets less restriction, so the gauge can show lower working pressure even when the pump is still moving water.

Glossary:

GPM: Gallons per minute, the US flow unit used by the nozzle-size formula.
PSI: Pounds per square inch, the pressure unit used for target and predicted pressure.
Orifice: The nozzle opening size expressed as the pressure-washer nozzle number.
Per-nozzle flow: Total pump flow divided by the number of identical nozzles sharing that flow.
Stocked orifice: A real nozzle size chosen near the exact calculated size.
Component rating: The lowest pressure rating among the pump, hose, gun, lance, couplers, and nozzle holder.
Bucket test: A practical flow check that measures washer output in a known time.

References:

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