Quick answer: Size a gas pipe from three things — the total connected load (sum the appliance ratings in BTU/h or m³/h), the longest run length, and the allowable pressure drop. Look the pipe size up in a gas sizing chart at your run length; capacity falls as the pipe gets longer. Do it instantly with the gas pipe sizing calculator.
The problem: a starved appliance at the end of the run
Every gas line drops pressure as it carries flow. Make the pipe too small (or the run too long) and the last appliance doesn't get its rated input — you see a lazy yellow flame, pilots that won't hold, or a geyser that never reaches temperature. Correct sizing guarantees every appliance its full BTU at the design pressure.
What you need to size a gas line
- Total load — add up every appliance's input rating (BTU/h; 1 m³/h natural gas ≈ 37,000 BTU/h).
- Longest run — the distance from the meter/regulator to the farthest appliance.
- Gas type & pressure — natural gas (low pressure, ~0.5 in.wc drop) vs LPG (higher pressure, denser).
- Allowable pressure drop — typically 0.5 in.wc for low-pressure NG systems.
Gas pipe sizing chart (natural gas, Schedule 40, indicative)
| Pipe size | Capacity at 20 ft (BTU/h) | Capacity at 60 ft (BTU/h) |
|---|---|---|
| 1/2" | 131,000 | 73,000 |
| 3/4" | 273,000 | 152,000 |
| 1" | 514,000 | 285,000 |
| 1-1/4" | 1,060,000 | 590,000 |
| 1-1/2" | 1,580,000 | 880,000 |
| 2" | 3,050,000 | 1,700,000 |
Indicative low-pressure natural-gas capacities (0.5 in.wc drop, 0.60 SG), aligned with NFPA 54 / IFGC. Capacity drops with length — always size at your actual longest run.
NG vs LPG
LPG (propane) packs about 2.5× the energy per unit volume of natural gas and usually runs at higher pressure, so the same BTU load needs a smaller pipe than natural gas — but it uses its own sizing tables. Never size an LPG line off a natural-gas chart.
Worked example
Appliances: cooktop 65,000 + geyser 40,000 + oven 45,000 Total load = 150,000 BTU/h Longest run = 65 ft At 60 ft: 3/4" carries ~152,000 BTU/h — right on the limit → step up to 1" (285,000 BTU/h) for a safe margin
Sizing on the 20 ft column (where 3/4" looks fine at 273,000) would have starved the run. Always read the chart at the real length.
Common mistakes
- Sizing on connected load but the wrong (short) length — capacity collapses on long runs.
- Forgetting fittings — each elbow/tee adds equivalent length.
- Mixing NG and LPG charts.
- Ignoring future appliances — leave headroom.
FAQ
What size gas pipe for a house? Add every appliance's BTU/h, take the longest run, and read the pipe size from the chart — commonly 3/4" to 1" for a domestic natural-gas system. Confirm with the gas pipe sizing calculator.
Does pipe length affect gas pipe size? Yes — longer runs drop more pressure, so a longer line needs a larger pipe for the same load.
Is LPG pipe smaller than natural gas? Usually yes, because LPG carries more energy per unit volume — but size it from an LPG table, not an NG one.