Add appliances in BTU/h or kW, enter the longest run, and get the Schedule 40 steel pipe size for natural gas or propane — using the IFGC / NFPA 54 sizing equations for low-pressure and 2 psi systems.
For trunk and branch sizing apply the same length to every section with that section's own load. Gas installations must be designed and installed by licensed persons in line with the adopted fuel gas code and the gas utility's rules.
| Size | ID | Capacity | Status |
|---|
Gas pipe is sized so that, at full load, the pressure lost between the meter and the farthest appliance stays within the allowance — usually 0.5 in. w.c. in a low-pressure system. The fuel gas codes give this as tables, and the same numbers come from their sizing equations:
| Size | 10 ft | 20 ft | 30 ft | 50 ft | 80 ft | 100 ft | 150 ft | 200 ft |
|---|---|---|---|---|---|---|---|---|
| 1/2″ | 173 | 119 | 96 | 72 | 56 | 50 | 40 | 34 |
| 3/4″ | 362 | 249 | 200 | 152 | 118 | 104 | 84 | 72 |
| 1″ | 682 | 469 | 377 | 286 | 222 | 196 | 158 | 135 |
| 1-1/4″ | 1,401 | 963 | 774 | 587 | 455 | 403 | 324 | 277 |
| 1-1/2″ | 2,100 | 1,443 | 1,159 | 880 | 682 | 605 | 486 | 416 |
| 2″ | 4,046 | 2,781 | 2,234 | 1,695 | 1,314 | 1,165 | 936 | 801 |
Calculated with the IFGC low-pressure equation; values match IFGC Table 402.4(2) within rounding. 1 ft³/h of natural gas ≈ 1,000 BTU/h.
Measure the run from the meter (or second-stage regulator) to the farthest appliance. Every section of the system is then sized with that one length, but with the load that section actually carries — the main for all appliances, each branch for its own. It is simple and conservative, which is why both IFGC and NFPA 54 use it as the default method.
Natural gas, low pressure, furnace 80,000 + water heater 40,000 + range 65,000 BTU/h, longest run 60 ft.
Add up the BTU/h input of all appliances, divide by 1,000 to get cubic feet per hour, measure the length to the farthest appliance, and pick the smallest pipe whose capacity at that length is at least the load from the code table or sizing equation.
In Schedule 40 steel with natural gas at 0.5 in. w.c. drop, about 172,000 BTU/h at 10 ft, 72,000 at 50 ft and 50,000 at 100 ft. Capacity falls quickly with length.
Propane carries about 2.5 times as much energy per cubic foot, so the same BTU load needs much less gas flow. It is also usually supplied at a higher pressure (11 in. w.c.).
A system that distributes gas at 2 psi to a regulator near the appliances, which drops it to normal appliance pressure. The higher pressure lets much smaller pipe — often CSST — carry the same load over long runs.
No. CSST capacities depend on the manufacturer's EHD rating and must be taken from their tables; copper tube has different inside diameters. This tool covers Schedule 40 steel pipe.
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