Gas Line Size Calculator

ANA›Life Services Authority›National Calculator Authority›Gas Line Size Calculator

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Gas Line Size Calculator

Determine the required pipe diameter for natural gas or propane distribution lines using the Spitzglass formula (low-pressure) and the Weymouth formula (high-pressure).

Flow Rate (CFH - cubic feet per hour)

Pipe Length (feet)

Allowable Pressure Drop (inches W.C.)

Gas Specific Gravity (air = 1.0)

Formula Type

Spitzglass Low-Pressure (< 1 PSI) Spitzglass High-Pressure (≥ 1 PSI) Weymouth (High-Pressure Transmission)

Inlet Pressure P1 (PSIA)

Outlet Pressure P2 (PSIA)

Calculate Required Pipe Diameter Results will appear here.

(function() { const formulaSelect = document.getElementById('gas-formula-type'); const inletGroup = document.getElementById('gas-inlet-pressure-group'); const outletGroup = document.getElementById('gas-outlet-pressure-group'); const pressureDropGroup = document.getElementById('gas-pressure-drop').closest('.calc-group');

formulaSelect.addEventListener('change', function() { const val = this.value; if (val === 'spitzglass_high' || val === 'weymouth') { inletGroup.style.display = ''; outletGroup.style.display = ''; pressureDropGroup.style.display = 'none'; } else { inletGroup.style.display = 'none'; outletGroup.style.display = 'none'; pressureDropGroup.style.display = ''; } });

window.gasCalc = function() { const resultDiv = document.getElementById('gas-result');

const Q = parseFloat(document.getElementById('gas-flow-rate').value); const L = parseFloat(document.getElementById('gas-pipe-length').value); const Sg = parseFloat(document.getElementById('gas-specific-gravity').value); const formula = document.getElementById('gas-formula-type').value;

// Validate common inputs if (isNaN(Q) || Q ⚠ Please enter a valid flow rate greater than 0.'; return; } if (isNaN(L) || L ⚠ Please enter a valid pipe length greater than 0.'; return; } if (isNaN(Sg) || Sg 3.0) { resultDiv.innerHTML = '⚠ Please enter a valid specific gravity between 0.1 and 3.0.'; return; }

let D = null; let formulaUsed = ''; let pressureInfo = '';

if (formula === 'spitzglass_low') { // Spitzglass Low-Pressure Formula: // Q = 3550 * sqrt( (deltaH * D^5) / (Sg * L * (1 + 3.6/D + 0.03*D)) ) // Solved iteratively for D const deltaH = parseFloat(document.getElementById('gas-pressure-drop').value); if (isNaN(deltaH) || deltaH ⚠ Please enter a valid pressure drop greater than 0.'; return; }

// Rearranged: Q^2 = 3550^2 * (deltaH * D^5) / (Sg * L * (1 + 3.6/D + 0.03D)) // f(D) = 3550^2 * deltaH * D^5 / (Sg * L * (1 + 3.6/D + 0.03D)) - Q^2 = 0 // Use Newton-Raphson iteration const K = (3550 * 3550 * deltaH) / (Sg * L); const Q2 = Q * Q;

let d = 1.0; // initial guess in inches let converged = false; for (let i = 0; i ⚠ Calculation did not converge. Please check your inputs.'; return; } D = d; formulaUsed = 'Spitzglass Low-Pressure'; pressureInfo = 'Pressure Drop: ' + deltaH.toFixed(3) + ' in. W.C.';

} else if (formula === 'spitzglass_high') { // Spitzglass High-Pressure Formula: // Q = 3550 * sqrt( (P1^2 - P2^2) * D^5 / (Sg * L * (1 + 3.6/D + 0.03*D)) ) const P1 = parseFloat(document.getElementById('gas-inlet-pressure').value); const P2 = parseFloat(document.getElementById('gas-outlet-pressure').value); if (isNaN(P1) || P1 ⚠ Please enter a valid inlet pressure.'; return; } if (isNaN(P2) || P2 = P1) { resultDiv.innerHTML = '⚠ Outlet pressure must be less than inlet pressure and greater than 0.'; return; }

const deltaP2 = P1 * P1 - P2 * P2; const K = (3550 * 3550 * deltaP2) / (Sg * L); const Q2 = Q * Q;

let d = 1.0; let converged = false; for (let i = 0; i ⚠ Calculation did not converge. Please check your inputs.'; return; } D = d; formulaUsed = 'Spitzglass High-Pressure'; pressureInfo = 'P1: ' + P1.toFixed(2) + ' PSIA, P2: ' + P2.toFixed(2) + ' PSIA, ΔP²: ' + deltaP2.toFixed(2) + ' PSIA²';

} else if (formula === 'weymouth') { // Weymouth Formula: // Q = 433.5 * (Tb/Pb) * sqrt( (P1^2 - P2^2) / (Sg * T * L * Z) ) * D^(8/3) // Simplified at standard conditions (Tb=520°R, Pb=14.73 psia, T=520°R, Z=1): // Q = 433.5 * (520/14.73) * sqrt( (P1^2 - P2^2) / (Sg * L) ) * D^(8/3) // Constant C = 433.5 * 520 / 14.73 ≈ 15301.4 // Q = C * sqrt( (P1^2 - P2^2) / (Sg * L) ) * D^(8/3) // D^(8/3) = Q / (C * sqrt(...)) // D = (Q / (C * sqrt(...)))^(3/8) const P1 = parseFloat(document.getElementById('gas-inlet-pressure').value); const P2 = parseFloat(document.getElementById('gas-outlet-pressure').value); if (isNaN(P1) || P1 ⚠ Please enter a valid inlet pressure.'; return; } if (isNaN(P2) || P2 = P1) { resultDiv.innerHTML = '⚠ Outlet pressure must be less than inlet pressure and greater than 0.'; return; }

const deltaP2 = P1 * P1 - P2 * P2; const C = 433.5 * 520.0 / 14.73; // ~15,301.4 const sqrtTerm = Math.sqrt(deltaP2 / (Sg * L)); if (sqrtTerm === 0) { resultDiv.innerHTML = '⚠ Invalid pressure or length values resulting in zero flow capacity.'; return; } D = Math.pow(Q / (C * sqrtTerm), 3.0 / 8.0); formulaUsed = 'Weymouth'; pressureInfo = 'P1: ' + P1.toFixed(2) + ' PSIA, P2: ' + P2.toFixed(2) + ' PSIA, ΔP²: ' + deltaP2.toFixed(2) + ' PSIA²'; }

if (D === null || isNaN(D) || D ⚠ Could not compute a valid pipe diameter. Please check your inputs.'; return; }

// Convert to common pipe sizes (nominal pipe sizes in inches - ID approximations) const nominalSizes = [ {nom: '1/2"', id: 0.622}, {nom: '3/4"', id: 0.824}, {nom: '1"', id: 1.049}, {nom: '1-1/4"', id: 1.380}, {nom: '1-1/2"', id: 1.610}, {nom: '2"', id: 2.067}, {nom: '2-1/2"', id: 2.469}, {nom: '3"', id: 3.068}, {nom: '4"', id: 4.026}, {nom: '6"', id: 6.065}, {nom: '8"', id: 7.981}, {nom: '10"', id: 10.020}, {nom: '12"', id: 11.938} ];

let recommended = null; for (let s of nominalSizes) { if (s.id >= D) { recommended = s; break; } }

const Dmm = D * 25.4; const Dcm = D * 2.54;

let pipeRow = recommended
? 'Recommended Nominal Pipe Size' + recommended.nom + ' (ID: ' + recommended.id.toFixed(3) + '")'
'Recommended Nominal Pipe SizeLarger than 12" — consult engineer';

resultDiv.innerHTML = '### ✓ Results ' + '' + 'ParameterValue' + 'Formula Used' + formulaUsed + '' + 'Flow Rate' + Q.toFixed(1) + ' CFH' + 'Pipe Length' + L.toFixed(1) + ' ft' + 'Specific Gravity' + Sg.toFixed(3) + '' + '' + (pressureInfo.includes('Drop') ? 'Pressure Drop' : 'Pressure Conditions') + '' + pressureInfo + '' + 'Calculated Minimum Inside Diameter' + D.toFixed(4) + ' in (' + Dmm.toFixed(2) + ' mm)' + pipeRow + '' + 'ⓘ Always select the next standard pipe size larger than the calculated minimum diameter. Verify with local codes (NFPA 54, IFGC, or applicable standard).

'; }; })();

#### Formulas Used

Spitzglass Low-Pressure (< 1 PSI):

Q = 3550 × √[ (ΔH × D&sup5;) / (Sg × L × (1 + 3.6/D + 0.03D)) ]

Spitzglass High-Pressure (≥ 1 PSI):

Q = 3550 × √[ (P&sub1;² − P&sub2;²) × D&sup5; / (Sg × L × (1 + 3.6/D + 0.03D)) ]

Weymouth (High-Pressure Transmission):

Q = 433.5 × (Tb/Pb) × √[ (P&sub1;² − P&sub2;²) / (Sg × T × L × Z) ] × D8/3

Where: Q = flow rate (CFH), D = inside diameter (in), L = pipe length (ft), Sg = specific gravity of gas (air=1.0), ΔH = pressure drop (in. W.C.), P&sub1; = inlet pressure (PSIA), P&sub2; = outlet pressure (PSIA), Tb = base temperature (520 °R), Pb = base pressure (14.73 PSIA), T = flowing temperature (520 °R), Z = compressibility factor (1.0 assumed)

#### Assumptions & References

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