Pipe Size & Water Velocity Calculator

ANA›Life Services Authority›National Calculator Authority›Pipe Size & Water Velocity Calculator

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Pipe Size & Water Velocity Calculator

Calculate pipe inner diameter, water velocity, or volumetric flow rate using the continuity equation Q = A × V for circular pipes.

Solve For

Water Velocity (V) Pipe Inner Diameter (D) Flow Rate (Q)

Flow Rate (Q)

m³/s L/s L/min m³/h GPM (US) CFM

Pipe Inner Diameter (D)

mm cm m inches feet

Water Velocity (V)

m/s ft/s km/h mph

Calculate

function pipToggleFields() { var solveFor = document.getElementById('pip-solve-for').value; document.getElementById('pip-group-flowrate').style.display = (solveFor === 'flowrate') ? 'none' : 'flex'; document.getElementById('pip-group-diameter').style.display = (solveFor === 'diameter') ? 'none' : 'flex'; document.getElementById('pip-group-velocity').style.display = (solveFor === 'velocity') ? 'none' : 'flex'; document.getElementById('pip-result').innerHTML = ''; }

function pipToM3s(val, unit) { if (unit === 'm3s') return val; if (unit === 'lps') return val / 1000; if (unit === 'lpm') return val / 60000; if (unit === 'm3h') return val / 3600; if (unit === 'gpm') return val * 6.30902e-5; if (unit === 'cfm') return val * 4.71947e-4; return val; }

function pipToMeters(val, unit) { if (unit === 'mm') return val / 1000; if (unit === 'cm') return val / 100; if (unit === 'm') return val; if (unit === 'in') return val * 0.0254; if (unit === 'ft') return val * 0.3048; return val; }

function pipToMs(val, unit) { if (unit === 'ms') return val; if (unit === 'fts') return val * 0.3048; if (unit === 'kmh') return val / 3.6; if (unit === 'mph') return val * 0.44704; return val; }

function pipFmt(val, decimals) { decimals = decimals || 4; if (Math.abs(val) >= 1e6 || (Math.abs(val) 3.0) return '⚠️ Velocity above 3.0 m/s — risk of erosion and noise.'; return '✅ Velocity within recommended range (0.3 – 3.0 m/s).'; }

function pipCalc() { var solveFor = document.getElementById('pip-solve-for').value; var resultDiv = document.getElementById('pip-result'); var errors = [];

var Q_val, Q_unit, D_val, D_unit, V_val, V_unit; var Q_m3s, D_m, V_ms;

if (solveFor !== 'flowrate') { Q_val = parseFloat(document.getElementById('pip-flowrate').value); Q_unit = document.getElementById('pip-flowrate-unit').value; if (isNaN(Q_val) || Q_val 0) { resultDiv.innerHTML = ''; return; }

var A_m2, result_label, result_value, result_unit, extra_rows = '';

if (solveFor === 'velocity') { // V = Q / A, A = π/4 × D² A_m2 = Math.PI / 4 * D_m * D_m; V_ms = Q_m3s / A_m2; result_label = 'Water Velocity (V)'; result_value = pipFmt(V_ms, 4); result_unit = 'm/s'; extra_rows += 'Velocity (ft/s)' + pipFmt(V_ms / 0.3048, 4) + ' ft/s'; } else if (solveFor === 'diameter') { // D = sqrt(4Q / (π × V)) A_m2 = Q_m3s / V_ms; D_m = Math.sqrt(4 * Q_m3s / (Math.PI * V_ms)); result_label = 'Pipe Inner Diameter (D)'; result_value = pipFmt(D_m * 1000, 2); result_unit = 'mm'; extra_rows += 'Diameter (inches)' + pipFmt(D_m / 0.0254, 3) + ' in'; extra_rows += 'Diameter (m)' + pipFmt(D_m, 5) + ' m'; } else { // Q = A × V, A = π/4 × D² A_m2 = Math.PI / 4 * D_m * D_m; Q_m3s = A_m2 * V_ms; result_label = 'Flow Rate (Q)'; result_value = pipFmt(Q_m3s, 6); result_unit = 'm³/s'; extra_rows += 'Flow Rate (L/s)' + pipFmt(Q_m3s * 1000, 4) + ' L/s'; extra_rows += 'Flow Rate (L/min)' + pipFmt(Q_m3s * 60000, 3) + ' L/min'; extra_rows += 'Flow Rate (m³/h)' + pipFmt(Q_m3s * 3600, 4) + ' m³/h'; extra_rows += 'Flow Rate (GPM)' + pipFmt(Q_m3s / 6.30902e-5, 3) + ' GPM'; }

var Re = pipReynolds(V_ms, D_m); var regime = pipFlowRegime(Re); var warning = pipVelocityWarning(V_ms);

resultDiv.innerHTML = '### Results ' + '' + '' + result_label + '' + result_value + ' ' + result_unit + '' + extra_rows + 'Cross-sectional Area (A)' + pipFmt(A_m2, 6) + ' m²' + 'Pipe Inner Diameter' + pipFmt(D_m * 1000, 2) + ' mm (' + pipFmt(D_m / 0.0254, 3) + ' in)' + 'Flow Rate (Q)' + pipFmt(Q_m3s, 6) + ' m³/s (' + pipFmt(Q_m3s * 1000, 4) + ' L/s)' + 'Velocity (V)' + pipFmt(V_ms, 4) + ' m/s (' + pipFmt(V_ms / 0.3048, 4) + ' ft/s)' + 'Reynolds Number (Re)' + pipFmt(Re, 0) + '' + 'Flow Regime' + regime + '' + '' + '' + warning + '

'; }

// Initialize field visibility pipToggleFields();

#### Formulas Used

Continuity Equation:

Q = A × V

where A = (π / 4) × D²

Therefore:

Reynolds Number: Re = (V × D) / ν

where ν = 1.004 × 10⁻⁶ m²/s (kinematic viscosity of water at 20°C)

#### Assumptions & References

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References

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