Nozzle sizing calculator
Enter your machine's pressure and flow. You get the orifice size to order and the spray angles worth keeping on the truck.
Work out your nozzle size
Enter your machine's pressure and flow rate. Numbers update as you type.
Nozzle numbers are rated at 4,000 PSI. Flow scales with the square root of pressure — which is why the same nozzle moves less water on a weaker machine.
to order
Why the number changes with your machine
Nozzle numbers are rated at 4,000 PSI. That is the convention the whole industry uses, and it is the reason the same nozzle behaves differently on two machines.
Flow through an orifice scales with the square root of pressure. So a nozzle that flows 4 GPM at 4,000 PSI flows about 3.5 GPM at 3,000 — which means if you buy a nozzle sized off your GPM alone and your machine runs below 4,000 PSI, you are running undersized and losing pressure at the surface.
The formula the calculator uses is the standard one: nozzle size = GPM × √(4,000 ÷ PSI).
Sizing up rather than down
If the number lands between two available sizes, go up rather than down. An undersized nozzle raises pressure at the pump, which is exactly the load your unloader and thermal relief exist to manage — and asking those parts to do that job every day is how they fail early.
An oversized nozzle costs you some pressure at the surface. An undersized one costs you a pump.
Nozzles wear, and nothing looks wrong
Orifices erode from the inside out. There is no visible damage, no leak, and no noise — just a machine that seems a bit weaker than it did last spring.
If your pressure has drifted down over a season, put a new nozzle on before you diagnose anything else. It costs a few dollars and it is the answer more often than any other single part.