Plumbing Pipe Size and Flow Rate Calculator

ANA›Life Services Authority›National Calculator Authority›Plumbing Pipe Size and Flow Rate 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; } }

Plumbing Pipe Size and Flow Rate Calculator

Calculate pipe flow rate, velocity, and required pipe diameter using the Hazen-Williams equation and basic fluid dynamics.

Calculation Mode

Find Flow Rate (given pipe diameter) Find Required Pipe Diameter (given flow rate)

Pipe Inner Diameter (inches)

Desired Flow Rate (GPM)

Pipe Length (feet)

Available Head Loss / Pressure Drop (psi)

Hazen-Williams C Factor

150 – PEX / Plastic (smooth) 140 – Copper / New Steel 130 – Galvanized Steel (new) 120 – Cast Iron (new) 100 – Cast Iron (old) 80 – Corroded / Old Steel

Calculate

function pluToggleMode() { var mode = document.getElementById('plu-calc-mode').value; document.getElementById('plu-group-diameter').style.display = (mode === 'flow') ? '' : 'none'; document.getElementById('plu-group-flowrate').style.display = (mode === 'diameter') ? '' : 'none'; document.getElementById('plu-result').style.display = 'none'; }

function pluCalc() { var resultDiv = document.getElementById('plu-result'); resultDiv.style.display = 'none';

var mode = document.getElementById('plu-calc-mode').value; var L = parseFloat(document.getElementById('plu-length').value); var psi = parseFloat(document.getElementById('plu-head-loss').value); var C = parseFloat(document.getElementById('plu-c-factor').value);

// Validate common inputs if (isNaN(L) || L 8) { velWarning = '⚠ Velocity exceeds 8 ft/s — risk of pipe erosion and noise.

'; } else { velWarning = '✔ Velocity is within the recommended range (2–8 ft/s).

'; }

html = '### Results ' + '' + 'ParameterValue' + 'Flow Rate' + Q.toFixed(2) + ' GPM (' + Q_lpm.toFixed(2) + ' L/min)' + 'Flow Velocity' + V_fps.toFixed(2) + ' ft/s (' + V_ms.toFixed(2) + ' m/s)' + 'Pipe Inner Diameter' + d.toFixed(3) + ' in' + 'Head Loss' + hf.toFixed(3) + ' ft (' + psi.toFixed(2) + ' psi)' + 'Friction Slope (S)' + S.toFixed(6) + ' ft/ft' + 'Hazen-Williams C' + C + '' + '' + velWarning;

} else { // Find diameter var Q_desired = parseFloat(document.getElementById('plu-flowrate').value); if (isNaN(Q_desired) || Q_desired = d_calc) { recommended = standardSizes[i]; recommendedLabel = standardLabels[i]; break; } } if (recommended === null) { recommended = d_calc; recommendedLabel = 'Custom (>8")'; }

// Actual flow with recommended size var Q_actual = 0.4322 * C * Math.pow(recommended, 2.63) * S054;

// Velocity with recommended size var r_ft2 = (recommended / 12) / 2; var A_ft2b = Math.PI * r_ft2 * r_ft2; var Q_ft3s2 = Q_desired * 0.002228; var V_fps2 = Q_ft3s2 / A_ft2b; var V_ms2 = V_fps2 * 0.3048;

var velWarning2 = ''; if (V_fps2 8) { velWarning2 = '⚠ Velocity exceeds 8 ft/s — risk of pipe erosion and noise.

'; } else { velWarning2 = '✔ Velocity is within the recommended range (2–8 ft/s).

'; }

html = '### Results ' + '' + 'ParameterValue' + 'Minimum Required Inner Diameter' + d_calc.toFixed(3) + ' in' + 'Recommended Standard Pipe Size (ID)' + recommendedLabel + ' (' + recommended.toFixed(3) + ' in ID)' + 'Capacity of Recommended Pipe' + Q_actual.toFixed(2) + ' GPM' + 'Velocity at Desired Flow' + V_fps2.toFixed(2) + ' ft/s (' + V_ms2.toFixed(2) + ' m/s)' + 'Head Loss' + hf.toFixed(3) + ' ft (' + psi.toFixed(2) + ' psi)' + 'Friction Slope (S)' + S.toFixed(6) + ' ft/ft' + 'Hazen-Williams C' + C + '' + '' + velWarning2; }

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

function pluShowError(msg) { var resultDiv = document.getElementById('plu-result'); resultDiv.innerHTML = '⚠ ' + msg + '

'; resultDiv.style.display = 'block'; }

#### Formula

Hazen-Williams Equation (Flow Rate):

Q = 0.4322 × C × d2.63 × S0.54

Required Diameter:

d = (Q / (0.4322 × C × S0.54))1/2.63

Flow Velocity:

V = Q / A  where  A = π × (d/2)2

#### Assumptions & References

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References

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