Guide · Nozzle tips and turbo nozzles
Which nozzle size fits your machine's PSI and GPM
Put your machine's rated PSI and GPM into the formula Cat Pumps and General Pump publish, then pick the nearest size its maker sells. Worked examples inside.
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Short answer
Put your machine's rated PSI and GPM into the formula Cat Pumps and General Pump publish: nozzle number = GPM x √(4,000 / PSI). Then choose the nearest size your machine's maker sells. Use the rated output, not the headline maximum, when the maker lists both. A nozzle size never makes a machine stronger.
The formula
Cat Pumps and General Pump both publish the same relationship: nozzle number = GPM x √(4,000 / PSI).[1] The nozzle number is the flow the nozzle passes at 4,000 PSI, so the formula scales your machine's flow to that reference pressure.[2]
Use paired working values: the flow at that pressure, not a maximum PSI combined with a maximum GPM. The formula links one flow to one pressure, so the two figures must come from the same operating point.
Why rated output, not the maximum
Many electric machines list two pairs of figures, and they are not one operating point.
- The 2020 Sun Joe SPX3000 manual (revision MR12) lists 2,030 PSI and 1.76 GPM maximum, and 1,450 PSI and 1.24 GPM rated working output.[3]
- Westinghouse lists the ePX3500 at 2,500 max PSI and 1.76 max GPM, and 2,000 rated PSI and 1.2 rated GPM.[4]
- Greenworks Commercial rates the GPW2300 (SKU 5107502VT) at 2,300 PSI at 1.2 GPM, with 2.3 GPM maximum flow measured at only 100 PSI.[5] Greenworks Canada lists the GPW2303A at 2,300 PSI maximum, 2.3 GPM maximum flow and 1.2 GPM rated flow.[6] These figures belong to those models and regions only.
- CRAFTSMAN rates the CMEPW2100 at 2,100 max PSI and 1.2 GPM, both measured with the 15-degree nozzle.[7]
Kärcher says its residential machines range from 1.25 to 2.5 GPM depending on the model, so look up your own model's figure.[8] More on reading spec sheets in max vs rated PSI and GPM.
Worked examples
All sizes below are calculated with the formula Cat Pumps and General Pump publish, from the maker's rated figures, and rounded.
| Machine | Rated PSI | Rated GPM | Calculated size |
|---|---|---|---|
| Sun Joe SPX3000 (MR12 manual) | 1,450 | 1.24 | about 2.1 |
| Westinghouse ePX3500 | 2,000 | 1.2 | about 1.7 |
| Greenworks GPW2300 (SKU 5107502VT) | 2,300 | 1.2 | about 1.6 |
Take the SPX3000. √(4,000 / 1,450) is about 1.66, and 1.66 x 1.24 is about 2.1. If you used the maximum pair instead (2,030 PSI and 1.76 GPM), you would get about 2.5, a size the machine's working output does not support. That is why the rated pair matters.
These numbers are a starting point for comparing tips, not a replacement for the maker's own parts list. If your machine's maker sells replacement tips, those are the size it designed for.
What the makers recommend
Some makers name a range or a size class directly.
- Active says its Active 2.0 ships with size 3.7 nozzles and recommends sizes from 3.5 to 5.0 for that machine.[9] That advice is for the Active 2.0 only.
- DEWALT sells its five-tip quick-connect sets in size 3.0 rated to 3,400 PSI (DXPA34ST) and size 4.0 rated to 4,500 PSI (DXPA45ST).[10] The PSI figure is the set's ceiling. Your machine must stay below it, and the size must still suit your machine's flow.
Too big or too small
The chart shows what happens when flow and size do not match. On General Pump's chart, a size 4 nozzle flows 4.00 GPM at 4,000 PSI but only about 2.83 GPM at 2,000 PSI.[11] Run the formula the other way (PSI = (GPM / nozzle number)² x 4,000) and 1.2 GPM through a size 3.0 tip comes out at about 640 PSI, calculated.[1] A nozzle far too large for the flow cannot build pressure.
Too small is not a free gain either. Generac's manual links a pulsing trigger to excessive pump pressure, typically caused by a clogged or restricted nozzle.[12] Cat Pumps says to verify that the pump's rated flow and pressure suit the nozzle.[2]
Worn nozzles
Cat Pumps' troubleshooting guide names worn nozzles as the most frequent cause of low pressure, and the fix is to replace them with the proper size.[13] A worn orifice is a larger orifice, which is the "too big" case above. See low or pulsing pressure for the other checks.
Approved tip sets
Picks that fit3 products
Choose by the size your calculation and your maker point to. SIMPSON 80145 is the size 3.0 set; SIMPSON 80146 and DEWALT DXPA45ST are size 4.0 sets.
More on choosing
These sizes suit higher-flow gas machines; for a low-flow electric machine, start with the maker's own replacement tips. Keep the set's PSI rating above your machine's. On Amazon, check that Ships from / Sold by is Amazon.com or the brand.
SIMPSON five-tip set, smaller of two sizes
SIMPSON 80145 1/4 in quick-connect nozzle set, 5 tips, size 3.0, 3,600 PSI
SIMPSON five-tip set, larger of two sizes
SIMPSON 80146 1/4 in quick-connect nozzle set, 5 tips, size 4.0, 4,500 PSI
Five-tip set in size 4.0
DEWALT DXPA45ST 4,500 PSI quick-connect spray tips, 5 tips, size 4.0, stainless steel
Next
Questions
What size nozzle do I need for a 1.2 GPM pressure washer?
It depends on the rated pressure that goes with that 1.2 GPM. With the formula Cat Pumps and General Pump publish, 1.2 GPM at 2,000 PSI works out to about size 1.7, and 1.2 GPM at 2,300 PSI to about size 1.6. Start from the size your machine's maker sells closest to that number.[1]
Should I use max or rated GPM?
Use the rated pair when the maker gives both. Cat Pumps and General Pump say to use paired working values, and makers such as Sun Joe and Westinghouse list maximum figures that are not the working point.[1][3][4]
What happens if the nozzle is too big?
The same flow passes through a larger hole at lower pressure. A size 4 nozzle flows about 4.00 GPM at 4,000 PSI but only about 2.83 GPM at 2,000 PSI on General Pump's chart, so a machine with far less flow cannot build its rated pressure through it.[11]
What happens if the nozzle is too small or clogged?
Generac's manual links a pulsing trigger to excessive pump pressure, typically from a clogged or restricted nozzle. Cat Pumps also says to verify that the pump's rated flow and pressure suit the nozzle.[12][2]
Can I turn up the pressure to make up for a worn nozzle?
No. Cat Pumps warns never to adjust the pressure regulating valve to compensate for worn nozzles, because it can over-pressurize and damage the pump. Replace the nozzle with the proper size.[13]