Gas Pipe Sizing Calculator

Natural gas or propane — Schedule 40 metallic and CSST from IFGC Table 402.4 capacity tables by BTU load, developed length, and fittings

Starting point, not gospel — verify against the locally adopted fuel gas code before installing or modifying gas piping. Pipe sizing in this tool follows the capacity-table method used by NFPA 54 (National Fuel Gas Code) / ANSI Z223.1 Chapter 6 and IFGC Section 402: Tables 402.4(2) (natural gas Schedule 40 metallic), 402.4(28) (undiluted propane Schedule 40), 402.4(15) (natural gas CSST at 0.5 in. w.c.), and 402.4(32) (propane CSST). Where the IRC is adopted for dwellings, see IRC Section G2413 and IRC Table G2413.4(1) for Schedule 40 natural gas. Equivalent-length fitting adders are field approximations. Meter capacity, regulator settings, elevation, and manufacturer CSST charts can control. This is not a permit drawing and not a substitute for the code book on the job.

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Gas Line Leak Check & Manometer Gear

After you size the pipe, prove the joints and the pressure. Leak detectors, bubble solution, thread compound, and manometers from the live TestTalkHQ affiliate CSV only.

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Audible/visual sniff test along joints, CSST fittings, and appliance connectors after a pressure test or a repair.

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Brush-on bubble solution for threaded joints and flare fittings when the electronic sniffer is quiet but you still want eyes on the joint.

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RectorSeal Tru-Blu

Listed pipe-thread compound for metallic gas pipe. Pair with NPT makeup from the NPT calculator — compound is not a substitute for correct thread engagement.

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Fieldpiece SDMN5 Dual-Port Manometer

Inches of water column at the meter, manifold, and appliance inlet — the field check after a capacity table says the pipe is big enough.

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Dwyer Series 475 Mark III digital manometer

Dwyer 475 Mark III Manometer

Handheld differential pressure for standing and operating pressure checks on natural gas and propane systems.

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How to Use This Gas Pipe Sizing Calculator

Sum the nameplate input ratings on the segment you are sizing. Measure the pipe path length. Count 90° elbows and branch tees (or enter a known equivalent length). Pick natural gas or propane and Schedule 40 metallic or CSST. Read the minimum size, table capacity, and the length row used after rounding up.

Developed length (steel) = measured + elbows×2.5 + tees×5.0
Developed length (CSST) = measured + max(0, elbows−4)×1.3 + tees×1.3
Table length = next IFGC row ≥ developed length
Size = smallest diameter / EHD with capacity ≥ load

Worked example — 100,000 BTU/hr natural gas, Schedule 40, 40 ft, no fittings Developed = 40 ft → 40 ft row. 1/2" holds 81 CFH (81,000 BTU/hr) — fails. 3/4" holds 170 CFH (170,000 BTU/hr) — 3/4".

Worked example — 40,000 BTU/hr natural gas, Schedule 40, 15 ft 15 ft rounds up to the 20 ft row. 1/2" holds 118 CFH (118,000 BTU/hr) ≥ 40,000 — 1/2".

Full method and steel vs CSST notes: guide. If burners starve or pressure drops on long runs: troubleshooting.

Gas Pipe Sizing FAQ

Why is there no chart page?

The calculator already embeds the IFGC Table 402.4 capacity rows used here. A standalone reprint would only restate those lookup tables without adding a reference the widget and guide do not already give you.

Is longest-length the only legal method?

No. NFPA 54 / IFGC also allow branch-length (and hybrid) sizing. This tool implements the longest-length capacity-table approach. Comparison: longest vs branch.

Do fittings really add that much length?

Yes for steel — elbows and tees are equivalent lengths in the developed-length total. CSST tables already bake in a limited bend allowance; extras still add length. Undercounting fittings is a classic starvation cause.

Natural gas or propane — can I use the same size?

No. Different tables, different energy density. Always pick the correct gas type before you trust the diameter.

Gas Pipe Sizing Calculator