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

Enter total connected appliance input (BTU/hr), measured length, elbow and tee counts, gas type, and steel or CSST. The calculator builds developed length, rounds up to the next table row, and returns the smallest listed size whose capacity covers the load. Walkthrough: gas pipe sizing guide. Field failures: troubleshooting. Method choice: longest vs branch length. Related loads: furnace sizing, water heater sizing. Plumbing index: hub.

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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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.

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What This Number Is (and Is Not)

The size is the smallest listed Schedule 40 diameter or CSST EHD in the selected IFGC Table 402.4 family whose capacity at the rounded-up length meets or exceeds the BTU load you typed. Natural gas Schedule 40 uses cubic feet per hour converted at 1000 BTU/cu ft. Propane tables are already in thousands of BTU per hour.

It is not a branch-length worksheet (that can allow smaller pipe on short branches). It is not a meter or regulator sizing tool. It is not permission to ignore manufacturer CSST charts, elevation corrections, or a different pressure-drop table in the adopted code. Thread makeup for steel fittings: NPT pipe thread calculator.

Input BTU, not output. Furnace and water-heater catalogs list input. AFUE or recovery efficiency does not shrink the gas pipe. Size the pipe to the burner, then size the appliance to the house with the furnace or water heater tools.

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

How to Use This Gas Pipe Sizing Calculator