Construction Calculators
Pressure Washer Nozzle Size Calculator
Enter your machine's GPM and PSI to get the nozzle orifice size, the pressure at the two nearest standard sizes, or work backward from a nozzle you already own.
Inputs
Result
Fill the form and press Calculate.
Safety: the calculated pressure must never exceed the rated pressure of your pump, hose, gun, and wand. Nozzle sizes are stamped by the maker and vary slightly, so confirm against your nozzle chart.
How it works
Nozzle size is the flow, in GPM, that the orifice passes at 4000 PSI. So a size 4.0 nozzle passes 4 GPM at 4000 PSI.
- Size = GPM × √(4000 ÷ PSI)
- GPM = size × √(PSI ÷ 4000)
- PSI = 4000 × (GPM ÷ size)²
Sizes are commonly sold in 0.5 steps (2.0 to 8.0 here), so an exact result is usually between two. A smaller size gives higher pressure at the same flow; a larger size gives lower pressure. Example: 3.5 GPM at 3000 PSI needs size 4.04, so a 4.0 nozzle runs at about 3,062 PSI and a 4.5 at about 2,420 PSI. The 3,062 PSI figure is above the 3,000 PSI rating of that machine, so the 4.5 is the safe pick.
Sources: APW nozzle calculator (PWNA nozzle formula, 0.5 size increments) and the Spraywell nozzle size chart (April 2023), whose values this calculator reproduces. Estimates only; not an engineering or safety approval.
FAQ
How do you calculate pressure washer nozzle size?
Nozzle size = GPM × square root of (4000 ÷ PSI). A size 4.0 nozzle passes 4 GPM at 4000 PSI. Common sizes come in 0.5 steps; confirm against your nozzle maker's chart.
What if my result falls between two nozzle sizes?
Pick a listed size and read the resulting pressure. A smaller number gives higher pressure and a larger number gives lower pressure at the same flow. Never exceed the pump, hose, or gun pressure rating.
How do I size nozzles for a surface cleaner?
Enter the number of nozzles. The total GPM is divided evenly across them and the size is calculated per nozzle.