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Gas pipe sizing calculator

Add up the appliance inputs, choose the gas and system pressure and enter the pipe length. The calculator finds the smallest commercial size that keeps pressure drop and velocity within limits.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

Pre-sizing
Gas

Defaults: natural gas 1,000 Btu/ft³ and 0.60; propane 2,516 Btu/ft³ and 1.52, as in the IFGC tables. Appliance ratings in the U.S. are on an HHV basis.

Gas appliances
Piping

Schedule 40 steel pipe (ASME B36.10M). The allowable drop changes with the pressure option: 0.5 in w.c. for a 7 in w.c. system, 1 psi for a 2 psi system, as in the IFGC sizing tables.

Monthly use
—Minimum gas pipe size
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Pressure drop by pipe size

Drop over the total length (actual + equivalent) at design flow. Green points pass; the dashed line is the allowable drop.

Tap the chart to see the values.

Pressure along the line

Gas pressure from the inlet to the farthest appliance, in the chosen size and one size smaller.

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Commercial pipe sizes (Schedule 40 steel)

Next step

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Method, assumptions and references

Equations used

Flow: Q = Σ(Pi · ni) × diversity ÷ heating value [m³/h; kW × 3.6 ÷ (MJ/m³)]
Pole (low pressure): h = s · L · Q² ÷ (0.0071² · d⁵) [mbar; m; m³/h; mm]
IFGC/NFPA 54 Eq. 4-1: D = Q^0.381 ÷ (19.17 · (ΔH ÷ (Cr · L))^0.206) [in; cfh; in w.c.; ft]; Cr = 0.6094 (natural gas), 1.2462 (propane)
Renouard linear: ΔP = 23,200 · s · L · Q^1.82 ÷ D^4.82 [mbar]
Renouard quadratic: P1² − P2² = 48.6 · s · L · Q^1.82 ÷ D^4.82 [bar absolute]; valid for Q ÷ D < 150
Velocity: v = Q · Patm ÷ (Patm + P2) ÷ (π · d² ÷ 4), at end-of-line pressure

Assumptions and limits

  • A single run from the meter or regulator to the farthest appliance carrying the full flow. For branched systems, size section by section with each section’s cumulative flow (longest-length method).
  • Flow at the heating value reference conditions (standard cubic feet); gas temperature in the line equal to the reference.
  • Pole and Renouard constants are the usual European forms. The IFGC and NFPA 54 use their own sizing tables and equations, which give smaller capacities for large pipe; check the final design against the adopted code.

Standards and technical documents

  • International Code Council: International Fuel Gas Code, Section 402.4, Equation 4-1 (low-pressure gas formula)
  • Renouard, P.: formules de calcul des réseaux de gaz (forma simplificada usada em manuais de distribuidoras europeias)
  • Pole, W.: low-pressure gas flow formula, as given in CIBSE/IPHE guides
  • ASME B36.10M: Welded and Seamless Wrought Steel Pipe
  • ISO 6976: Natural gas — Calculation of calorific values, density and relative density
  • GPSA Engineering Data Book, section 17 (fluid flow and piping)

U.S. regulations

  • NFPA 54 / ANSI Z223.1: National Fuel Gas Code (pipe sizing, Chapter 6 tables and equations; testing and purging)
  • International Fuel Gas Code (IFGC), Section 402: pipe sizing; Section 406: inspection, testing and purging
  • Local utility service rules and the authority having jurisdiction

Frequently asked questions

How do I get gas flow from appliance input?

Divide input by heating value. A 400,000 Btu/h burner on natural gas at 1,000 Btu/ft³ uses 400 ft³/h; on propane at 2,516 Btu/ft³, about 159 ft³/h.

What pressure drop is allowed in a gas line?

The IFGC and NFPA 54 require the appliance to get at least its minimum inlet pressure. Code sizing tables for 7 in w.c. systems are based on a 0.5 in w.c. drop; tables for 2 psi systems use a 1 psi drop.

When should I use Pole and when Renouard?

Pole and Renouard linear suit low pressure, up to about 30 in w.c. Above that, use Renouard quadratic, which accounts for gas density changing with pressure.

Why does propane need a smaller pipe than natural gas?

Propane carries about 2.5 times more energy per cubic foot, so the same input needs much less flow. Its higher specific gravity raises the drop, but the lower flow wins.