Pressure Washer Nozzle Size Calculator
Enter your pressure washer's flow and target working pressure to calculate the theoretical nozzle/orifice size and compare nearby common standard nozzle sizes.
Calculate nozzle size
Results are theoretical and assume clean water. Always stay within the pressure and flow ratings of your pump, gun, hose, fittings and nozzle.
Machine inputs
Use the machine's actual flow if you know it. Target PSI should be the working pressure you want at the nozzle.
For multi-nozzle surface cleaners, use the dedicated Surface Cleaner Nozzle Calculator when it is published. This tool is for one pressure-washer nozzle using the machine's total GPM.
What this calculator returns
You'll get the exact theoretical nozzle size, the nearest size from a common General Pump nozzle chart, and the estimated pressure produced by that standard size at your entered GPM.
A smaller orifice generally raises pressure demand; a larger orifice lowers pressure. Actual pressure can differ because of pump condition, unloader settings, hose loss, fittings and water supply.
Nearby standard sizes
How to calculate pressure washer nozzle size
Pressure-washer nozzle sizing is based on the relationship between flow and pressure. A nozzle size is a flow-capacity number, not the spray angle. For pressure-washer sizing, a commonly used relationship is:
For example, a 4 GPM machine targeting 3,000 PSI produces a theoretical nozzle size of about 4.62. A nearby stocked size may be 4.5, which would theoretically produce slightly more than 3,000 PSI at 4 GPM. The calculator shows that estimated difference so you can make an informed selection.
Why the exact result and the stocked nozzle can differ
Nozzle calculations often produce a number between commonly stocked sizes. Choosing the next smaller or larger size changes the theoretical pressure. The best choice depends on the equipment ratings and the pressure you actually want, not just which number is mathematically closest.
Does spray angle change the orifice size?
The spray pattern and orifice size are separate characteristics. Common pressure-washer tips may use different spray angles while sharing the same orifice size. Select the spray pattern appropriate for the surface and cleaning task.
What if my current nozzle is a different size?
Enter its size in the optional comparison field. The calculator estimates the pressure that nozzle would require at the entered GPM. This is a theoretical comparison; actual system pressure may be lower because of real-world losses and pump limitations.
Pressure washer nozzle size questions
What nozzle size do I need for 4 GPM at 4,000 PSI?
The theoretical nozzle size is 4.0. A size 4 nozzle is also a common standard chart size.
What happens if the nozzle is too large?
At the same flow, a larger nozzle requires less pressure. Cleaning force may decrease, although the larger orifice can be useful when intentionally reducing pressure.
What happens if the nozzle is too small?
A smaller nozzle requires higher pressure to pass the same flow. The pump or unloader may prevent the machine from reaching that theoretical condition, and using an undersized nozzle can place unnecessary stress on equipment. Never exceed equipment ratings.
Is this the right calculator for a surface cleaner?
Not if the surface cleaner splits machine flow across two or more nozzles. That calculation should divide total GPM across the tips. A dedicated Surface Cleaner Nozzle Calculator is planned for this site.
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Formula and chart references
This calculator uses the standard pressure-washer nozzle relationship documented by Dultmeier Sales and common standard sizes shown in General Pump's 2025 nozzle chart. These references support the theoretical sizing math; they do not replace the equipment manufacturer's operating instructions.
Dultmeier pressure washer nozzle size reference · General Pump nozzle chart