Pressure Washer Nozzle Size Calculator

Washer preset:

Choose a common starting setup, then edit any value that differs from your equipment.

Pump flow:

Enter open-trigger pump output, not the faucet supply rating.

Target working pressure:

The nozzle formula sizes the opening for this flowing pressure.

Nozzles sharing flow:

Each nozzle is sized from an equal share of total pump flow.

Spray pattern:

Select the pattern you plan to buy or replace.

Stocked-size choice:

Choose how the exact hydraulic size should map to an available General Pump chart size.

Lowest component rating:

The result warns when the selected stocked tip predicts pressure above this limit.

Pressure tolerance:

Use a tighter band when pressure matching matters more than stocked-size convenience.

±{{ pressure_tolerance_percent }}%

Orifice wear allowance:

Zero models a new tip and is neutral.

{{ wear_allowance_percent }}%

Measured bucket-test flow:

This comparison does not replace pump flow in the nozzle formula.

Metric	Value	Interpretation	Copy
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Read the stocked-size result

The exact hydraulic size is {{ exactOrificeDisplay }}; the selected chart strategy recommends {{ stockedOrificeDisplay }} and predicts {{ predictedPressureDisplay }}. The selected spray pattern produces tip code {{ computation.values.tip_code }}. {{ statusDetail }}

Check the complete pressure path

Keep predicted pressure below the lowest rating among the pump, unloader, hose, gun, lance, couplers, and tip holder. Never treat a smaller tip as a safe way to exceed a component rating.

Account for wear and measurement

Formula boundary

Nozzle size = per-nozzle GPM × √(4000 ÷ target PSI). General Pump chart sizes are used for the stocked match; verify critical setups with the equipment manual and an open-trigger pressure gauge.

A pressure-washer tip carries two separate specifications. The spray angle controls how concentrated the water pattern is, while the orifice size controls how much flow can pass at a given pressure. Changing the angle changes surface impact and coverage. Changing the orifice changes the hydraulic resistance seen by the pump.

The common nozzle-size scale is referenced to gallons per minute (GPM) at 4,000 pounds per square inch (PSI). A size 4.0 orifice passes about 4 GPM at 4,000 PSI. Pressure changes with the square of flow divided by orifice size, so a small step to a tighter tip can raise pressure sharply. A larger tip lowers predicted pressure.

Pump flow: Open-trigger output from the pump, not the building's faucet supply rating.
Working pressure: Pressure while water is flowing through the installed hose, gun, and nozzle.
Stocked orifice: A purchasable chart size chosen near the exact hydraulic result.

Multi-nozzle attachments divide total pump flow. A 4 GPM surface cleaner with two equal nozzles is sized at 2 GPM per nozzle, not 4 GPM through each tip. Ignoring that split usually selects openings that are too large and produces weak or uneven cleaning.

Wear moves in the same direction as choosing a larger opening. As the orifice erodes, the same pump flow produces less pressure. A bucket test can reveal that actual flow differs from the nameplate, but it does not replace the pump-flow value in the sizing formula unless the measured result truly represents open-trigger pump output.

Nozzle sizing is a selection aid, not a safety certification. The gun, hose, fittings, unloader, attachment, and nozzle must all be rated for the possible pressure. Confirm the completed setup with manufacturer guidance and a suitable gauge, and begin on a low-risk test area because a correct hydraulic match can still damage a delicate surface.

How to Use This Tool:

Match the setup as it will operate with the trigger open.

Choose a Washer preset or Custom, then replace its values with the pump plate, manual, gauge, or measured data for your equipment.
Enter Pump flow in GPM or L/min, Target working pressure in PSI or bar, and the number of equal Nozzles sharing flow.
Select the Spray pattern and a Stocked-size choice. Nearest minimizes size difference; next larger lowers predicted pressure; next smaller raises it.
Enter the Lowest component rating. Adjust pressure tolerance and wear allowance only when those assumptions match the job. Add bucket-test flow when you want a comparison with the stated pump output.
Check the exact and stocked sizes, predicted pressure, status, and tip code. Stop if predicted pressure is over any component rating, and verify low- or high-pressure choices before installation.

Interpreting Results:

Exact orifice is the continuous hydraulic result. Stocked orifice is the chart size selected by the chosen strategy. The stocked size determines Predicted pressure and the tip code; the exact size is not necessarily sold.

On target includes both tolerance boundaries. High pressure and Low pressure apply only outside that band. Over rating takes priority whenever predicted pressure is greater than the lowest component rating, even if it would otherwise be inside the target tolerance.

Wear projection shows the pressure expected from a larger effective opening at the same flow. A measured-flow difference is diagnostic evidence, not an automatic correction. Confirm unexpected results by checking inlet supply, filters, hose restriction, unloader behavior, nozzle condition, and gauge placement.

Technical Details:

The hydraulic calculation uses GPM and PSI internally. Liters per minute are divided by 3.785411784, and bar is multiplied by 14.503773773. Total flow is divided equally among one to four nozzles before sizing.

Formula Core

Per-nozzle flow q equals total pump flow Q divided by nozzle count N. Exact orifice O uses the 4,000 PSI chart reference:

O = \frac{Q}{N} \sqrt{\frac{4000}{P}}

Once stocked size O_s is chosen, predicted pressure follows the inverse-square relationship:

P_{pred} = 4000 {(\frac{q}{O_{s}})}^{2}

Wear allowance w increases the stocked opening before pressure is recalculated:

O_{worn} = O_{s} (1 + w)

Lookup Core

Supported stocked sizes are 2, 2.5, 3, 3.25, 3.5, 3.75, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 12.5, 13, 14, 15, 20, 25, 30, 40, 50, and 60. Results outside this chart are rejected.

Nearest chooses the smallest absolute size difference; an exact tie stays with the lower size.
Next larger chooses the first stocked size greater than or equal to the exact result.
Next smaller chooses the last stocked size less than or equal to the exact result.

Rule Core

Pressure washer nozzle status rules in precedence order
Status	Exact rule
Over rating	Predicted pressure > lowest component rating.
High pressure	Predicted pressure > target × (1 + tolerance).
Low pressure	Predicted pressure < target × (1 − tolerance).
On target	Predicted pressure is inside or exactly on both tolerance boundaries.

Safety and Accuracy Notes:

The chart relationship assumes stable flow and does not model pressure loss through hoses, guns, fittings, filters, surface-cleaner swivels, or other restrictions. Pump wear, inlet starvation, unloader adjustment, gauge location, and unequal nozzle flow can move actual pressure away from the estimate.

Target pressure must remain within the 40 to 5,000 PSI chart range.
Use the lowest rating among every pressurized component, not the pump's advertised maximum alone.
Do not use a smaller tip to compensate for a pump, inlet, or unloader fault.
Depressurize equipment before changing tips and follow the equipment manufacturer's operating instructions.

Worked Examples:

A dual-nozzle surface cleaner

A 4 GPM pump feeding two equal nozzles supplies 2 GPM per tip. At a 3,000 PSI target, the exact size is about 2.309. The nearest stocked size is 2.5, which predicts 2,560 PSI, or 14.67% below target. With an 8% tolerance, the result is Low pressure, and a 25-degree tip is coded 25025. The example shows why dividing flow before choosing each bar nozzle is essential.

References:

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