Gas Pipe Size Calculator
Size natural gas or propane pipe with the NFPA 54 / IFGC longest-length method. Enter the total BTU load and the longest run to get the minimum Schedule 40 pipe size and its capacity in CFH. Free, no sign-up.
What to calculate next
Tools commonly used alongside this calculation
Drainage Fixture Unit (DFU) Calculator
Size sanitary drainage pipe from drainage fixture units. Add fixtures to total the DFU load, then get the minimum building drain, branch, or stack size per IPC Table 710.1. Free, no sign-up.
Drain Slope Calculator
Calculate drain pipe slope for DWV and sewer lines. Find the total fall from a run and pitch, or the slope from a measured drop, and check it against the IPC minimum grade by pipe size. Free, no sign-up.
Explanation
A gas pipe has to be large enough to deliver the full demand of every appliance it serves without dropping the pressure below what those appliances need. This calculator follows the longest-length method of NFPA 54 (the National Fuel Gas Code) and the International Fuel Gas Code (IFGC) — the standard sizing routine adopted across the United States. Enter the connected load in BTU per hour and the longest run, and it returns the minimum Schedule 40 pipe size and the flow it can carry.
How the longest-length method works
First convert the connected load from heat input (BTU per hour) to a gas flow rate in cubic feet per hour (CFH) by dividing by the heating value of the gas. Then measure the longest developed length — the run from the meter or regulator to the most distant appliance, plus an allowance for fittings — and size every segment using that single length. Sizing for the worst-case run keeps the pressure drop within the table's limit everywhere in the system.
| Term | Meaning |
|---|---|
| Load | Sum of appliance input ratings the segment serves (BTU/hr) |
| Heating value | Energy per cubic foot — about 1,000 BTU/ft³ for natural gas, 2,516 for propane |
| CFH | Required gas flow, cubic feet per hour |
| Length | Longest developed run; round up to the next length in the table |
With the required CFH and the design length in hand, read down the capacity table and pick the smallest pipe whose capacity at that length meets or exceeds the flow. When the measured length falls between two columns, always use the next longer column — never interpolate.
Schedule 40 pipe capacity (natural gas)
The values below are from IFGC Table 402.4(2) / NFPA 54 — Schedule 40 metallic pipe, natural gas of 0.60 specific gravity, a 0.5 in. w.c. pressure drop, and an inlet pressure below 2 psi. Each number is the capacity in CFH; this is the abbreviated set of lengths the calculator uses the full table behind.
| Pipe size | 10 ft | 50 ft | 100 ft | 150 ft | 200 ft |
|---|---|---|---|---|---|
| 1/2 in | 172 | 72 | 50 | 40 | 34 |
| 3/4 in | 360 | 151 | 104 | 83 | 71 |
| 1 in | 678 | 284 | 195 | 157 | 134 |
| 1-1/4 in | 1,390 | 583 | 400 | 322 | 275 |
| 1-1/2 in | 2,090 | 873 | 600 | 482 | 412 |
| 2 in | 4,020 | 1,680 | 1,160 | 928 | 794 |
| 2-1/2 in | 6,400 | 2,680 | 1,840 | 1,480 | 1,270 |
| 3 in | 11,300 | 4,740 | 3,260 | 2,610 | 2,240 |
Propane carries fewer cubic feet per hour because it is denser. The code lets you reuse the natural gas table by multiplying every capacity by a gravity factor (IFGC A.2.4) — for propane (specific gravity 1.5) that factor is about 0.633. The calculator applies it automatically when you select propane.
Typical appliance loads
The connected load is the sum of the input ratings stamped on the nameplate of every appliance the segment feeds. These representative ratings give a feel for typical demand; always use the actual nameplate values for design.
| Appliance | Typical input (BTU/hr) |
|---|---|
| Furnace (residential) | 100,000 |
| Tankless water heater | 199,000 |
| Storage water heater | 40,000 |
| Range / cooktop | 65,000 |
| Clothes dryer | 35,000 |
| Gas log / fireplace | 26,000 |
| Pool heater | 250,000 |
| Barbecue / grill | 50,000 |
Notes and limitations
This calculator covers Schedule 40 metallic pipe at a 0.5 in. w.c. pressure drop and a standard low-pressure (under 2 psi) system — the most common residential and light-commercial case. A 0.3 in. w.c. drop, a 2 psi system, CSST, or copper tube each use a different table. The longest-length method is deliberately conservative; an engineered branch-length design can sometimes justify a smaller pipe. Include a realistic fitting allowance in the run length, confirm the appliance demands, and always verify the result against the code edition and the authority having jurisdiction.