Gas pipe sizing calculator: what size gas pipe do I need?
3/4 in Schedule 40 pipe
150 cfh at 1,000 Btu/cu ft; 170 in the 40 ft row of Table 402.4(2) · for 150,000 Btu/h at 40 ft
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3/8 or 10' 6".
3/4 in Schedule 40 pipe
150 cfh at 1,000 Btu/cu ft; 170 in the 40 ft row of Table 402.4(2)
Source: International Fuel Gas Code 2021, Section 402.4 and Tables 402.4(2) and 402.4(28), read October 27, 2026. Read the source
Natural gas at 150,000 Btu/h over a 40 ft longest run takes 3/4 in Schedule 40 pipe: 150 cfh at 1,000 Btu per cu ft, and IFGC 2021 Table 402.4(2) gives 3/4 in 170 cfh at 40 ft.
A worked example
Propane to a 212,000 Btu/h section, with 73 ft from the second-stage regulator to the farthest appliance needs a 1 in Schedule 40 pipe. 73 ft is not a row of Table 402.4(28), so the 80 ft row counts. 212,000 Btu/h is 212 in thousands: there 3/4 in carries 197 and 1 in carries 372.
What size gas line for a furnace and a water heater?
A 100,000 Btu/h furnace and a 40,000 Btu/h water heater on one line are 140 cfh of natural gas at 1,000 Btu per cu ft. At 30 ft Table 402.4(2) gives 3/4 in, rated 199 cfh; at 60 ft the 3/4 in drops to 137 cfh and the line goes to 1 in.
How much gas can a 1/2 in line carry?
In natural gas, 172 cfh at 10 ft, 72 at 50 ft and 50 at 100 ft by Table 402.4(2). In propane, 291,000 Btu/h at 10 ft, 122,000 at 50 ft and 84,000 at 100 ft by Table 402.4(28).
Which length do I use for each section?
The longest one, every time: IFGC 402.4.1 sizes each section with the length from the meter or regulator to the farthest outlet and the load that section carries. A length between two rows takes the longer row, as Appendix A103.1 does.
What else it is called
Also searched as a gas line size calculator, natural gas pipe sizing chart or propane pipe sizing chart. The code calls the method the longest length method, and the input of an appliance is on its rating plate in Btu per hour.
Pipe capacity by length
| Longest length | 1/2 in | 3/4 in | 1 in | 1 1/4 in | 1 1/2 in | 2 in |
|---|---|---|---|---|---|---|
| 10 ft | 172 cfh · 291k | 360 cfh · 608k | 678 cfh · 1,150k | 1,390 cfh · 2,350k | 2,090 cfh · 3,520k | 4,020 cfh · 6,790k |
| 20 ft | 118 cfh · 200k | 247 cfh · 418k | 466 cfh · 787k | 957 cfh · 1,620k | 1,430 cfh · 2,420k | 2,760 cfh · 4,660k |
| 30 ft | 95 cfh · 160k | 199 cfh · 336k | 374 cfh · 632k | 768 cfh · 1,300k | 1,150 cfh · 1,940k | 2,220 cfh · 3,750k |
| 40 ft | 81 cfh · 137k | 170 cfh · 287k | 320 cfh · 541k | 657 cfh · 1,110k | 985 cfh · 1,660k | 1,900 cfh · 3,210k |
| 50 ft | 72 cfh · 122k | 151 cfh · 255k | 284 cfh · 480k | 583 cfh · 985k | 873 cfh · 1,480k | 1,680 cfh · 2,840k |
| 60 ft | 65 cfh · 110k | 137 cfh · 231k | 257 cfh · 434k | 528 cfh · 892k | 791 cfh · 1,340k | 1,520 cfh · 2,570k |
| 80 ft | 56 cfh · 94k | 117 cfh · 197k | 220 cfh · 372k | 452 cfh · 763k | 677 cfh · 1,140k | 1,300 cfh · 2,200k |
| 100 ft | 50 cfh · 84k | 104 cfh · 175k | 195 cfh · 330k | 400 cfh · 677k | 600 cfh · 1,010k | 1,160 cfh · 1,950k |
| 150 ft | 40 cfh · 67k | 83 cfh · 140k | 157 cfh · 265k | 322 cfh · 543k | 482 cfh · 814k | 928 cfh · 1,570k |
| 200 ft | 34 cfh · 58k | 71 cfh · 120k | 134 cfh · 227k | 275 cfh · 465k | 412 cfh · 697k | 794 cfh · 1,340k |
Each cell: natural gas in cubic feet per hour from IFGC 2021 Table 402.4(2) (under 2 psi, 0.5 in w.c. drop, 0.60 specific gravity) · undiluted propane in thousand Btu per hour from Table 402.4(28) (11 in w.c., 0.5 in w.c. drop). Schedule 40 metallic pipe. Both tables run from 10 to 2,000 ft and up to 12 in (natural gas) or 4 in (propane).
Where the numbers come from
- Sizes: International Fuel Gas Code 2021, Section 402.4 and Tables 402.4(2) and 402.4(28), as adopted by New Jersey, matching the 2021 Seattle Fuel Gas Code and IRC Table G2413.4(1). Table 402.4(2): natural gas, Schedule 40 metallic pipe, under 2 psi, 0.5 in w.c. pressure drop, 0.60 specific gravity, e.g. 1/2 in carries 172 cfh at 10 ft and 72 at 50 ft, 3/4 in 199 at 30 ft. Table 402.4(28): undiluted propane at 11 in w.c., 0.5 in w.c. drop, in thousand Btu/h, e.g. 1/2 in 291 at 10 ft. 402.4.1: size each section with the longest length from the point of delivery to the most remote outlet and the load of that section. Read October 27, 2026. IFGC 2021 chapter 4 on UpCodes
- Row and heating value: Appendix A of the 2021 Seattle Fuel Gas Code, the IFGC appendix, informative and not part of the code. A103.1: use the row of the measured length or the next longer length; A102.1: Btu/h ÷ the average heating value of the gas, which the gas supplier gives; the A106.1 example uses 1,000 Btu per cu ft. Read October 27, 2026. 2021 Seattle Fuel Gas Code, Appendix A (PDF)
- The rest is arithmetic: cfh = Btu/h ÷ heating value for natural gas; thousand Btu/h = Btu/h ÷ 1,000 for propane.
The two tables are for Schedule 40 metallic pipe: natural gas under 2 psi with a 0.5 in w.c. drop, and propane at 11 in w.c. past the second-stage regulator. CSST, copper and polyethylene, 2 psi systems and fittings counted as extra length use other tables; above 2,000 ft of elevation the flow is adjusted for altitude (402.2).
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