Gas Pipe Sizing Calculator
Size natural gas or propane piping with the IFGC low-pressure equation: connected load in kW or BTU/h, longest run, pressure drop, Schedule 40 steel or copper, minimum diameter and capacity table.
How it works
IFGC Eq. 4-1 (inlet < 1.5 psi): D = Q^0.381 ÷ [19.17 × (ΔH ÷ (Cr × L))^0.206] · Q = load ÷ heating value (ft³/h) · Cr = 0.6094 natural gas, 1.2462 propane · D in inches, L in ft, ΔH in inches of water column
Low-pressure gas piping is sized so that the pressure lost between the meter or regulator and the farthest appliance stays within the allowance — usually 0.5 inch of water column (125 Pa) for natural gas. The International Fuel Gas Code gives the low-pressure equation behind its capacity tables (Section 402.4, Eq. 4-1), using Cr = 0.6094 for natural gas and 1.2462 for undiluted propane. This calculator converts the total connected load to cubic feet per hour, solves for the minimum inside diameter and picks the first standard size whose inside diameter is at least that; it reproduces IFGC Table 402.4(2), where ½″ Schedule 40 carries 172 ft³/h over 10 ft. With the longest-length method, every section is sized for the load it carries using the length to the farthest outlet.
Worked example
A 60 kW natural gas load (204,728 BTU/h, about 205 ft³/h or 5.80 m³/h) with a 15 m (49.2 ft) longest run and a 0.5″ w.c. drop: D = 205^0.381 ÷ [19.17 × (0.5 ÷ (0.6094 × 49.2))^0.206] = 0.92″ (23.4 mm). The first Schedule 40 size with a larger inside diameter is 1″ · DN25 (1.049″), which carries 84.5 kW at this length; ¾″ would carry only 44.8 kW.
Sources: ICC — 2021 International Fuel Gas Code, Section 402.4 and Table 402.4(2) · NFPA 54 National Fuel Gas Code — Chapter 6 pipe sizing
Frequently asked questions
How do I size a gas line?
Add up the BTU/h (or kW) input of every appliance, measure the length from the meter to the farthest appliance, and read the smallest pipe whose capacity at that length is at least the load — or use the IFGC equation as this calculator does. Each branch is sized for its own load at the same longest length.
How many BTU can a 3/4 inch gas line carry?
About 360,000 BTU/h of natural gas over 10 ft, 151,000 over 50 ft and 104,000 over 100 ft for ¾″ Schedule 40 steel with a 0.5″ w.c. drop (IFGC Table 402.4(2)). Propane at 11″ w.c. carries more because each cubic foot holds about 2.5 times the energy.
What pressure drop should I use for gas pipe sizing?
0.5 inch of water column is the usual design drop for natural gas at 7″ w.c. supply; 0.3″ is used for long or sensitive systems, and 1″ or more for 2 psi and elevated-pressure systems with regulators.
Can I use this for propane?
Yes — choose propane. The equation uses its specific gravity (Cr = 1.2462) and about 2,516 BTU per cubic foot, so the same pipe carries more BTU/h than with natural gas.
Related calculators
Gas piping must be designed and installed by a licensed gas fitter under your local fuel gas code; this tool gives a first estimate.