Pressure washer · calculator
Pressure Washer Nozzle Size Calculator & Orifice Chart
Calculate nozzle size, cleaning units, and water consumption from pump GPM and operating PSI.
Method record
What this calculator measures
Nozzle orifice restriction creates backpressure against positive-displacement pump flow. Cleaning Units (PSI × GPM) quantify total washing capability, and runtime flow determines supply water requirements.
Nozzle Size = GPM × √(4000 ÷ PSI) | Cleaning Units = PSI × GPM Use it correctly
Calculation steps
- Find pump rated GPM and desired PSI.
- Match the calculated nozzle number to manufacturer spray tips.
- Verify that the water supply can sustain total job volume.
Applicability
Use the model within its limits
Spray tip color tags denote fan angle (0° Red, 15° Yellow, 25° Green, 40° White), not nozzle orifice size. Never undersize a nozzle below pump specifications.
What this result represents
- System
- Pressure washer
- Formula
- Nozzle Size = GPM × √(4000 ÷ PSI) | Cleaning Units = PSI × GPM
- Review
- Verify safety-sensitive work with qualified guidance.
Worked Field Example
Worked Example: Commercial Pressure Washer Orifice Selection
Field Scenario: Determining nozzle orifice size, cleaning units, and water consumption for a pressure washer pump rated at 3,500 PSI and 3.8 GPM.
Given Input Parameters
Step-by-Step Mathematical Solution
- Calculate Nozzle Size: Size = GPM × √(4,000 / PSI) = 3.8 × √(4,000 / 3,500) = 3.8 × 1.069 ≈ 4.06.
- Commercial selection: Select Size 4.0 or 4.5 orifice (Size 4.0 yields ~3,500 PSI at 3.75 GPM).
- Calculate Cleaning Units (CU): CU = 3,500 × 3.8 = 13,300 CU.
- Calculate Water Usage: Gallons = 3.8 GPM × 30 min = 114 gallons.
Nozzle Size 4.0; produces 13,300 Cleaning Units; consumes 114 gallons in 30 minutes.
Professional Guidance: Never install a nozzle smaller than Size 4.0 on this machine, as excessive backpressure will force the unloader into continuous bypass.
Engineering Standard Reference
Universal Pressure Washer Nozzle Sizing Chart (GPM vs PSI)
Match your pressure washer pump flow rate (GPM) and working pressure (PSI) to find the correct standard nozzle orifice size number:
| Pump Flow Rate (GPM) | 1,500 PSI | 2,000 PSI | 2,500 PSI | 3,000 PSI | 3,500 PSI | 4,000 PSI |
|---|---|---|---|---|---|---|
| 2.0 GPM | Size 3.0 | Size 3.5 | Size 4.0 | Size 4.5 | Size 4.8 | Size 5.5 |
| 2.5 GPM | Size 3.5 | Size 4.0 | Size 4.5 | Size 5.0 | Size 5.5 | Size 6.0 |
| 3.0 GPM | Size 4.0 | Size 4.5 | Size 5.0 | Size 5.5 | Size 6.0 | Size 6.5 |
| 3.5 GPM | Size 4.5 | Size 5.0 | Size 5.5 | Size 6.0 | Size 6.5 | Size 7.0 |
| 4.0 GPM | Size 5.0 | Size 5.5 | Size 6.0 | Size 6.5 | Size 7.0 | Size 7.5 |
| 4.5 GPM | Size 5.5 | Size 6.0 | Size 6.5 | Size 7.0 | Size 7.5 | Size 8.2 |
| 5.0 GPM | Size 6.0 | Size 6.5 | Size 7.0 | Size 7.5 | Size 8.0 | Size 9.0 |
Engineering Note: Nozzle code standard: First 2 digits = spray angle (00=0°, 15=15°, 25=25°, 40=40°), last 2 digits = orifice size (e.g. 2504 = 25° fan with size 4.0 orifice). An undersized tip causes unloader valve overheating.
Engineering FAQs
Frequently Asked Questions
How do I measure for a pressure washer nozzle (PSI and GPM)?
To measure your machine's true operating parameters: 1) Measure flow rate (GPM) by running water from the high-pressure wand into a 5-gallon bucket for exactly 60 seconds with no tip installed; gallons filled equals pump GPM. 2) Measure operating pressure (PSI) by inserting an inline 5,000 PSI gauge between the unloader outlet and high-pressure hose under full trigger spray. Use these two field measurements in the calculator above to select the exact nozzle orifice size.
What happens if I install a nozzle that is too small for my pressure washer?
Installing an undersized nozzle restricts flow below the pump's displacement rating, forcing the unloader valve into continuous bypass mode, overheating the pump manifold, and creating severe pressure spikes that can blow hoses or crack pump pistons.
What are Cleaning Units (CU) and why do they matter?
Cleaning Units (PSI × GPM) quantify the overall cleaning effectiveness and productivity of a pressure washer. While high PSI strips stubborn paint and cuts grease, high GPM flushes debris away. A machine with 3,000 PSI at 4 GPM (12,000 CU) cleans faster than a machine with 4,000 PSI at 2.5 GPM (10,000 CU).
What do pressure washer spray tip colors mean?
Industry-standard color coding designates spray fan angle: Red = 0° (concentrated pinpoint jet for cutting), Yellow = 15° (heavy stripping), Green = 25° (general cleaning and washing), White = 40° (wide wash for vehicles and siding), and Black = 65° (low-pressure chemical and detergent application).