Pressure Washer Nozzle Size Calculator

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Pressure Washer Nozzle Size Calculator

Determine the correct nozzle orifice size for your pressure washer based on your machine's flow rate (GPM) and operating pressure (PSI).

Flow Rate (GPM)

Gallons per minute output of your pressure washer pump

Operating Pressure (PSI)

Pounds per square inch at the nozzle

Calculate Nozzle Size

function preCalc() { var resultDiv = document.getElementById('pre-result'); var gpmInput = document.getElementById('pre-gpm'); var psiInput = document.getElementById('pre-psi');

var gpm = parseFloat(gpmInput.value); var psi = parseFloat(psiInput.value);

// --- Validation --- if (isNaN(gpm) || isNaN(psi)) { resultDiv.innerHTML = 'Please enter values for both Flow Rate and Pressure.'; return; } if (gpm 20) { resultDiv.innerHTML = 'Flow Rate must be between 0.1 and 20 GPM.'; return; } if (psi 10000) { resultDiv.innerHTML = 'Pressure must be between 100 and 10,000 PSI.'; return; }

/ * Nozzle Orifice Size Formula (industry standard): * * Nozzle Number = (GPM / sqrt(PSI / 1000)) * 100 * * This yields the standard nozzle "number" used by manufacturers * (e.g., 4.0 = size 04, 5.5 = size 05.5). * * Orifice Diameter (inches): * Q = GPM (flow rate) * Cd = 0.90 (discharge coefficient for a sharp-edged orifice, typical nozzle) * P = PSI (pressure) * ρ = 0.03613 lb/in³ (density of water) * g = 386.09 in/s² (gravitational acceleration) * * Velocity v = sqrt(2 * g * P / ρ) [in/s] * Area A = Q / (Cd * v * 231) [in²] (231 in³ per gallon) * Diameter d = sqrt(4 * A / π) [inches] * * Nozzle Number (manufacturer convention): * nozzleNum = (GPM / sqrt(PSI / 1000)) * 100 /

var Cd = 0.90; var rho = 0.03613; // lb/in³ var g = 386.09; // in/s² var pi = Math.PI;

// Velocity of water through orifice (in/s) var velocity = Math.sqrt(2 * g * psi / rho);

// Flow rate in in³/s (1 gallon = 231 in³, 1 min = 60 s) var Q_in3s = gpm * 231 / 60;

// Orifice area (in²) var area = Q_in3s / (Cd * velocity);

// Orifice diameter (inches) var diameter_in = Math.sqrt(4 * area / pi);

// Orifice diameter in mm var diameter_mm = diameter_in * 25.4;

// Standard nozzle number (manufacturer convention) var nozzleNum = (gpm / Math.sqrt(psi / 1000)) * 100;

// Round nozzle number to nearest 0.5 for standard sizing var nozzleNumRounded = Math.round(nozzleNum * 2) / 2;

// Determine closest standard nozzle size label var standardSizes = [1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 9.0, 10.0, 11.0, 12.0]; var closest = standardSizes[0]; var minDiff = Math.abs(nozzleNum - standardSizes[0]); for (var i = 1; i ' + 'ParameterValue' + 'Calculated Nozzle Number' + nozzleNum.toFixed(2) + '' + 'Closest Standard Nozzle Size' + sizeLabel + ' (' + closest.toFixed(1) + ')' + 'Orifice Diameter' + diameter_in.toFixed(4) + ' in (' + diameter_mm.toFixed(2) + ' mm)' + 'Orifice Area' + (area * 1000).toFixed(4) + ' × 10⁻³ in²' + 'Water Exit Velocity' + (velocity / 12).toFixed(1) + ' ft/s' + 'Cleaning Units (GPM × PSI)' + cleaningUnits.toFixed(0) + ' CU' + '' + 'Tip: Nozzle size ' + sizeLabel + ' means the orifice number is ' + sizeLabel + ' — look for this number stamped on the nozzle body. Always verify with your pump manufacturer's chart.

'; }

#### Formulas Used

1. Water Exit Velocity (Torricelli / Bernoulli):

v = √(2 · g · P / ρ)

2. Orifice Area:

A = Q / (Cd · v)

3. Orifice Diameter:

d = √(4A / π)

4. Manufacturer Nozzle Number (industry convention):

Nozzle Number = (GPM / √(PSI / 1000)) × 100

The nozzle number is printed on the nozzle (e.g., "40" = size 4.0). Multiply by 10 to get the stamped label (e.g., 4.0 → "040").

5. Cleaning Units:

CU = GPM × PSI

#### Assumptions & References

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