Pressure Washer GPM & PSI Flow Rate Calculator

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Pressure Washer GPM & PSI Flow Rate Calculator

Calculate Cleaning Units (CU), nozzle orifice size, and flow characteristics for your pressure washer using GPM and PSI values.

Flow Rate (GPM)

gallons per minute

Pressure (PSI)

pounds per square inch

Nozzle Angle (degrees)

0° (Red – Pinpoint) 15° (Yellow – Stripping) 25° (Green – General Cleaning) 40° (White – Delicate) 65° (Black – Soap/Low Pressure)

Nozzle Efficiency (%)

%

Calculate

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

var gpm = parseFloat(document.getElementById('pre-gpm').value); var psi = parseFloat(document.getElementById('pre-psi').value); var angle = parseFloat(document.getElementById('pre-nozzle-angle').value); var effPct = parseFloat(document.getElementById('pre-efficiency').value);

// --- Validation --- if (isNaN(gpm) || gpm 20) { resultDiv.innerHTML = 'Please enter a valid GPM between 0.1 and 20.

'; return; } if (isNaN(psi) || psi 10000) { resultDiv.innerHTML = 'Please enter a valid PSI between 100 and 10,000.

'; return; } if (isNaN(effPct) || effPct 100) { resultDiv.innerHTML = 'Please enter a nozzle efficiency between 50% and 100%.

'; return; }

var eff = effPct / 100.0;

// --- Core Calculations ---

// 1. Cleaning Units (CU) = GPM × PSI var cu = gpm * psi;

// 2. Hydraulic Power (HP) = (PSI × GPM) / 1714 // (1714 is the conversion factor: 1 HP = 1714 PSI·GPM) var hydraulicHP = (psi * gpm) / 1714.0;

// 3. Nozzle Orifice Area (in²) // Q = Cd × A × sqrt(2 × g × h) // In practical pressure washer form: // A (in²) = GPM / (29.84 × Cd × sqrt(PSI)) // where Cd (discharge coefficient) ≈ efficiency, 29.84 is unit conversion constant // (derived from Torricelli: Q[GPM] = 29.84 × Cd × A[in²] × sqrt(PSI)) var cd = eff; var nozzleArea = gpm / (29.84 * cd * Math.sqrt(psi)); // in²

// 4. Nozzle Orifice Diameter (inches) // A = π/4 × d² → d = sqrt(4A/π) var nozzleDiameter = Math.sqrt((4.0 * nozzleArea) / Math.PI); // inches var nozzleDiameterMM = nozzleDiameter * 25.4;

// 5. Exit Velocity (ft/s) // v = sqrt(2 × g × h) where h = pressure head // PSI to feet of head: h = PSI × 144 / 62.4 (water density 62.4 lb/ft³) // v (ft/s) = sqrt(2 × 32.174 × PSI × 144 / 62.4) × Cd var pressureHead = psi * 144.0 / 62.4; // feet of water var exitVelocity = cd * Math.sqrt(2.0 * 32.174 * pressureHead); // ft/s var exitVelocityMPH = exitVelocity * 0.681818;

// 6. Flow rate in liters per minute var lpm = gpm * 3.78541;

// 7. Water usage per hour var gph = gpm * 60.0;

// 8. Nozzle size code (industry standard: size = GPM/sqrt(PSI) × 100, rounded to nearest 0.5) // Standard nozzle sizing: nozzle number = (GPM / sqrt(PSI/1000)) × 10 // Common formula: size = round(GPM × sqrt(1000/PSI) × 10) / 10 var nozzleSizeRaw = gpm * Math.sqrt(1000.0 / psi) * 10.0; var nozzleSizeRounded = Math.round(nozzleSizeRaw * 2) / 2; // round to nearest 0.5

// 9. Determine pressure category var pressureCategory = ""; if (psi 3,300 PSI)";

// 10. Determine CU cleaning power category var cuCategory = ""; if (cu ' + 'ParameterValue' + 'Cleaning Units (CU)' + cu.toLocaleString(undefined,{maximumFractionDigits:0}) + ' CU' + 'Cleaning Power' + cuCategory + '' + 'Pressure Category' + pressureCategory + '' + 'Hydraulic Power' + hydraulicHP.toFixed(3) + ' HP' + 'Exit Velocity' + exitVelocity.toFixed(1) + ' ft/s (' + exitVelocityMPH.toFixed(1) + ' mph)' + 'Flow Rate (LPM)' + lpm.toFixed(2) + ' L/min' + 'Water Usage per Hour' + gph.toFixed(1) + ' GPH (' + (lpm*60).toFixed(0) + ' L/hr)' + 'Nozzle Orifice Area' + nozzleArea.toFixed(5) + ' in²' + 'Nozzle Orifice Diameter' + nozzleDiameter.toFixed(4) + ' in (' + nozzleDiameterMM.toFixed(2) + ' mm)' + 'Nozzle Size Code' + nozzleSizeRounded.toFixed(1) + ' (angle: ' + angleLabel + ')' + ''; }

#### Formulas Used

1. Cleaning Units (CU): CU = GPM × PSI

2. Hydraulic Power (HP): HP = (PSI × GPM) / 1714 (1 HP = 550 ft·lbf/s; 1 gallon = 231 in³; conversion yields 1714 PSI·GPM per HP)

3. Nozzle Orifice Area (Torricelli / Discharge Equation): Q = Cd × A × √(2gΔP/ρ) In practical units: A (in²) = GPM / (29.84 × Cd × √PSI) where 29.84 is the unit-conversion constant for water at standard conditions

4. Nozzle Orifice Diameter: d = √(4A / π)

5. Exit Velocity: v = Cd × √(2 × g × h) h (ft) = PSI × 144 / 62.4  (pressure head of water) g = 32.174 ft/s²

6. Nozzle Size Code (Industry Standard): Size = GPM × √(1000 / PSI) × 10, rounded to nearest 0.5

#### Assumptions & References

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References

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