Pipe Size & Flow Rate Calculator
ANA›Life Services Authority›National Calculator Authority›Pipe Size & Flow Rate Calculator
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Pipe Size & Flow Rate Calculator
Calculate volumetric flow rate, flow velocity, and pressure drop for circular pipes using the Hazen-Williams and Darcy-Weisbach equations.
### Pipe Geometry
Pipe Inner Diameter (inches)
Pipe Length (feet)
### Flow Parameters
Calculation Method
Hazen-Williams (water, turbulent) Darcy-Weisbach (general)
Hazen-Williams C Coefficient
150 – PVC / Plastic 140 – New Steel / Copper 130 – Welded Steel 120 – Cast Iron (new) 100 – Cast Iron (old) 80 – Concrete
Solve For
Flow Rate (given head loss) Head Loss (given flow rate)
Head Loss (feet of water)
Flow Rate (GPM)
Pipe Roughness ε (inches)
0.000059 – Drawn Tubing / PVC 0.0018 – Commercial Steel 0.0035 – Welded Steel 0.012 – Cast Iron 0.06 – Concrete
Fluid Kinematic Viscosity (cSt)
Solve For
Head Loss (given flow rate) Flow Rate (given head loss)
Flow Rate (GPM)
Head Loss (feet)
Calculate
#### Formulas Used
Hazen-Williams (flow rate from head loss):
Q = 0.4322 × C × D2.63 × S0.54
where S = hf / L (head loss per unit length), D = diameter (inches), C = roughness coefficient
Hazen-Williams (head loss from flow rate):
hf = 10.67 × L × Q1.852 / (C1.852 × D4.87)
where Q = flow rate (GPM), D = diameter (inches), L = length (feet)
Darcy-Weisbach:
hf = f × (L / D) × (V² / 2g)
Friction factor f via Colebrook-White equation (iterative):
1/√f = −2 log₁₀(ε/(3.7D) + 2.51/(Re√f))
Flow Velocity:
V = Q / A = Q / (π × (D/2)²)
Reynolds Number:
Re = V × D / ν
#### Assumptions & References
(function() {
/ ── toggle method panels ── / window.pipToggleMethod = function() { var m = document.getElementById('pip-method').value; document.getElementById('pip-hazen-inputs').style.display = (m === 'hazen') ? '' : 'none'; document.getElementById('pip-darcy-inputs').style.display = (m === 'darcy') ? '' : 'none'; };
window.pipToggleHWSolve = function() { var s = document.getElementById('pip-hw-solve').value; document.getElementById('pip-hw-headloss-input').style.display = (s === 'flow') ? '' : 'none'; document.getElementById('pip-hw-flow-input').style.display = (s === 'headloss') ? '' : 'none'; };
window.pipToggleDarcySolve = function() { var s = document.getElementById('pip-darcy-solve').value; document.getElementById('pip-darcy-flow-input').style.display = (s === 'headloss') ? '' : 'none'; document.getElementById('pip-darcy-hl-input').style.display = (s === 'flow') ? '' : 'none'; };
/ ── helpers ── / function getVal(id) { return parseFloat(document.getElementById(id).value); }
function showError(msg) { var el = document.getElementById('pip-result'); el.style.display = ''; el.innerHTML = '⚠ ' + msg + ''; }
function showResult(html) { var el = document.getElementById('pip-result'); el.style.display = ''; el.innerHTML = html; }
/ ── Colebrook-White friction factor (iterative) ── / function colebrookFriction(Re, relRoughness) { if (Re 0.'); return; } if (isNaN(L_ft) || L_ft 0.'); return; }
var D_ft = D_in / 12; var A_ft2 = Math.PI * Math.pow(D_ft / 2, 2); // cross-sectional area ft² var method = document.getElementById('pip-method').value;
var Q_gpm, V_fps, hf_ft, Re, f_val, regime, rows = '';
/ ════════════════════════════════ HAZEN-WILLIAMS ════════════════════════════════ / if (method === 'hazen') { var C = parseFloat(document.getElementById('pip-hw-c').value); var solve = document.getElementById('pip-hw-solve').value;
if (solve === 'flow') { // Q from head loss var hl = getVal('pip-hw-hl'); if (isNaN(hl) || hl 0.'); return; } var S = hl / L_ft; // slope ft/ft // Q (GPM) = 0.4322 * C * D^2.63 * S^0.54 Q_gpm = 0.4322 * C * Math.pow(D_in, 2.63) * Math.pow(S, 0.54); hf_ft = hl; } else { // head loss from Q var q = getVal('pip-hw-q'); if (isNaN(q) || q 0.'); return; } Q_gpm = q; // h_f = 10.67 * L * Q^1.852 / (C^1.852 * D^4.87) hf_ft = 10.67 * L_ft * Math.pow(Q_gpm, 1.852) / (Math.pow(C, 1.852) * Math.pow(D_in, 4.87)); }
// Convert Q to ft³/s: 1 GPM = 0.002228 ft³/s var Q_cfs = Q_gpm * 0.002228; V_fps = Q_cfs / A_ft2;
// Reynolds number using water kinematic viscosity 1.004 cSt = 1.081e-5 ft²/s var nu_water = 1.081e-5; Re = V_fps * D_ft / nu_water; regime = flowRegime(Re);
var Q_m3s = Q_cfs * 0.0283168; var Q_lpm = Q_gpm * 3.78541; var V_ms = V_fps * 0.3048; var hf_m = hf_ft * 0.3048; var hf_psi = hf_ft * 0.4335; // 1 ft water = 0.4335 psi
rows = 'Flow Rate' + Q_gpm.toFixed(2) + ' GPM' + Q_lpm.toFixed(2) + ' L/min' + 'Flow Velocity' + V_fps.toFixed(3) + ' ft/s' + V_ms.toFixed(3) + ' m/s' + 'Head Loss' + hf_ft.toFixed(3) + ' ft' + hf_m.toFixed(3) + ' m' + 'Pressure Drop' + hf_psi.toFixed(3) + ' psi' + (hf_psi * 6894.76 / 1000).toFixed(3) + ' kPa' + 'Reynolds Number' + Math.round(Re).toLocaleString() + ' (' + regime + ')' + 'H-W Coefficient (C)' + C + '';
showResult( '### Results – Hazen-Williams ' + 'ParameterImperialMetric' + rows + '' + (Re 0.'); return; } var nu_ft2s = nu_cst * 1.07639e-5; // cSt → ft²/s (1 cSt = 1e-6 m²/s; 1 m²/s = 10.7639 ft²/s)
var eps_in = parseFloat(document.getElementById('pip-roughness').value); var relRough = eps_in / D_in; // ε/D (both in inches)
var dSolve = document.getElementById('pip-darcy-solve').value; var g = 32.174; // ft/s²
if (dSolve === 'headloss') { // head loss from flow rate var dq = getVal('pip-darcy-q'); if (isNaN(dq) || dq 0.'); return; } Q_gpm = dq; var Q_cfs2 = Q_gpm * 0.002228; V_fps = Q_cfs2 / A_ft2; Re = V_fps * D_ft / nu_ft2s; if (Re 0.'); return; } hf_ft = dhl; V_fps = darcyFlowFromHL(D_ft, L_ft, hf_ft, nu_ft2s, relRough); Re = V_fps * D_ft / nu_ft2s; if (Re Flow Rate' + Q_gpm.toFixed(2) + ' GPM' + Q_lpm2.toFixed(2) + ' L/min' + 'Flow Velocity' + V_fps.toFixed(3) + ' ft/s' + V_ms2.toFixed(3) + ' m/s' + 'Head Loss' + hf_ft.toFixed(3) + ' ft' + hf_m2.toFixed(3) + ' m' + 'Pressure Drop' + hf_psi2.toFixed(3) + ' psi' + (hf_psi2 * 6.89476).toFixed(3) + ' kPa' + 'Reynolds Number' + Math.round(Re).toLocaleString() + ' (' + regime + ')' + 'Friction Factor (f)' + f_val.toFixed(5) + (Re ' + 'Relative Roughness (ε/D)' + relRough.toExponential(3) + '';
showResult( '### Results – Darcy-Weisbach ' + 'ParameterImperialMetric' + rows + '' ); } };
})();
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