Water Pressure & PSI Loss Calculator

ANA›Life Services Authority›National Calculator Authority›Water Pressure & PSI Loss Calculator

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Water Pressure & PSI Loss Calculator

Calculate static water pressure from elevation head, friction pressure loss using the Hazen-Williams equation, and net pressure at any point in a water distribution or plumbing system.

### System Parameters

Source / Inlet Pressure (PSI)

PSI

Elevation Change (ft) (positive = uphill, negative = downhill)

ft

### Pipe Parameters (Hazen-Williams Friction Loss)

Flow Rate (GPM)

GPM

Pipe Inside Diameter (inches)

in

Pipe Length (ft)

ft

Hazen-Williams C Coefficient

150 – PEX / Smooth Plastic (new) 140 – PVC / CPVC 130 – Copper (new) 120 – Galvanized Steel (new) 110 – Cast Iron (new) 100 – Cast Iron (old) 90 – Galvanized Steel (old) 80 – Concrete / Rough pipe Custom…

Custom C Value

Minor Losses – Fittings Equivalent Length (%)

% of pipe length

Calculate

(function() { // Show/hide custom C input document.getElementById('wat-hw-c').addEventListener('change', function() { document.getElementById('wat-custom-c-row').style.display = this.value === 'custom' ? 'flex' : 'none'; });

window.watCalc = function() { var resultDiv = document.getElementById('wat-result'); resultDiv.style.display = 'none';

// --- Read inputs --- var sourcePsi = parseFloat(document.getElementById('wat-source-psi').value); var elevation = parseFloat(document.getElementById('wat-elevation').value); var flow = parseFloat(document.getElementById('wat-flow').value); var diameter = parseFloat(document.getElementById('wat-diameter').value); var length = parseFloat(document.getElementById('wat-length').value); var hwSel = document.getElementById('wat-hw-c').value; var fittingsPct = parseFloat(document.getElementById('wat-fittings-pct').value);

var C = hwSel === 'custom'
? parseFloat(document.getElementById('wat-custom-c').value)
parseFloat(hwSel);

// --- Validation --- var errors = []; if (isNaN(sourcePsi) || sourcePsi 0 GPM.'); if (isNaN(diameter) || diameter 0 inches.'); if (isNaN(length) || length 0.'); if (isNaN(fittingsPct) || fittingsPct 0) { resultDiv.innerHTML = 'Please fix the following:' + errors.map(function(e){ return ''; }).join('') + ''; resultDiv.style.display = 'block'; return; }

// --- Calculations ---

// 1. Elevation pressure change: 1 ft of water = 0.4335 PSI // Uphill (positive elevation) REDUCES pressure; downhill ADDS pressure var PSI_PER_FT = 0.4335; var elevationPsiLoss = elevation * PSI_PER_FT; // positive = loss, negative = gain

// 2. Hazen-Williams friction loss (PSI per 100 ft) // h_f (ft/100ft) = 0.2083 * (100/C)^1.852 * Q^1.852 / d^4.8704 // Convert ft of head to PSI: divide by 2.3077 (1 PSI = 2.3077 ft H2O) var effectiveLength = length * (1 + fittingsPct / 100); var hwHeadPer100ft = 0.2083 * Math.pow(100 / C, 1.852) * Math.pow(flow, 1.852) / Math.pow(diameter, 4.8704); var hwHeadTotal = hwHeadPer100ft * (effectiveLength / 100); // ft of head var frictionPsiLoss = hwHeadTotal / 2.3077; // convert to PSI

// 3. Velocity in pipe // Area (ft²) = π/4 * (d/12)² // Flow (ft³/s) = GPM / 448.831 var areaSqFt = Math.PI / 4 * Math.pow(diameter / 12, 2); var flowCfs = flow / 448.831; var velocityFps = flowCfs / areaSqFt; // ft/s

// 4. Velocity pressure (minor – informational) // P_v = ρv²/2 ; in PSI: v²/(2g) ft head → PSI var velocityHeadFt = Math.pow(velocityFps, 2) / (2 * 32.174); var velocityPsi = velocityHeadFt / 2.3077;

// 5. Net outlet pressure var totalPsiLoss = elevationPsiLoss + frictionPsiLoss; var outletPsi = sourcePsi - totalPsiLoss;

// --- Format helpers --- function fmt(v, d) { return isNaN(v) ? 'N/A' : v.toFixed(d !== undefined ? d : 2); }

function statusBadge(psi) { if (psi >= 40) return '✔ Adequate (' + fmt(psi) + ' PSI)'; if (psi >= 20) return '⚠ Low (' + fmt(psi) + ' PSI)'; return '✘ Insufficient (' + fmt(psi) + ' PSI)'; }

// --- Build result HTML --- var html = '### Results '; html += ''; html += 'ParameterValue'; html += 'Source / Inlet Pressure' + fmt(sourcePsi) + ' PSI'; html += 'Elevation Pressure Change' + (elevationPsiLoss >= 0 ? '-' : '+') + fmt(Math.abs(elevationPsiLoss)) + ' PSI (' + (elevation >= 0 ? 'uphill loss' : 'downhill gain') + ')'; html += 'Effective Pipe Length (with fittings)' + fmt(effectiveLength, 1) + ' ft'; html += 'Friction Loss (Hazen-Williams)-' + fmt(frictionPsiLoss) + ' PSI'; html += 'Flow Velocity' + fmt(velocityFps, 2) + ' ft/s' + (velocityFps > 8 ? ' ⚠ High (>8 ft/s)' : '') + ''; html += 'Velocity Pressure Head' + fmt(velocityPsi, 3) + ' PSI'; html += 'Total PSI Loss' + fmt(totalPsiLoss) + ' PSI'; html += 'Net Outlet Pressure' + statusBadge(outletPsi) + ''; html += '';

if (outletPsi ⚠ Outlet pressure is negative — the system cannot deliver flow under these conditions. Increase source pressure, reduce flow, use a larger pipe, or shorten the run.'; } else if (outletPsi ⚠ Outlet pressure is below 20 PSI. Most fixtures require 20–80 PSI for proper operation.'; }

resultDiv.innerHTML = html; resultDiv.style.display = 'block'; }; })();

#### Formulas Used

Elevation Pressure Change: ΔPelev (PSI) = Elevation (ft) × 0.4335 PSI/ft (Positive elevation = uphill = pressure loss; negative = downhill = pressure gain)

Hazen-Williams Friction Loss: hf = 0.2083 × (100/C)1.852 × Q1.852 / d4.8704  [ft head per 100 ft] Friction Loss (PSI) = hf × Leff / 100 / 2.3077 where Q = flow (GPM), d = inside diameter (in), C = Hazen-Williams coefficient, Leff = pipe length × (1 + fittings %/100)

Flow Velocity: v (ft/s) = Q (ft³/s) / A (ft²)  |  Qft³/s = GPM / 448.831  |  A = π/4 × (d/12)²

Net Outlet Pressure: Pout = Psource − ΔPelev − ΔPfriction

#### Assumptions & References

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References

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