Gas pipe sizing calculator

Sizes low pressure natural gas piping in Schedule 40 steel pipe or copper tubing with the sizing equations of the 2024 International Fuel Gas Code, by the longest length or the branch length method. It runs in your browser. Nothing you enter is sent anywhere.

This calculator needs JavaScript. It runs fully in your browser and sends nothing to a server. The equations and sources are on the methodology page.

1. System

Gas and pipe

Gas

Pipe material

Pressure

Delivery pressure

Pressure at the point of delivery (meter outlet). Get it from your gas supplier. This tool covers systems below 1.5 psi only.

Minimum appliance inlet pressure (in. w.c.) The highest minimum inlet pressure among your appliances, from the rating plates or the installation instructions. In inches water column, not psi.

Maximum appliance inlet pressure (in. w.c.), optional The lowest maximum inlet pressure among your appliances, from the rating plates. If the delivery pressure is above it, a line pressure regulator is required (IFGC 410.1) and no result is shown.

Allowable pressure drop The drop must leave at least the minimum inlet pressure at every appliance (IFGC 402.6).

Gas supply data

Heating value (Btu per cubic foot) 1,000 is the value the IFGC Appendix A examples assume. Use the value from your gas supplier.

Elevation of the job (ft), optional Above 2,000 ft the code requires an altitude adjustment that this tool does not perform.

2. Pipe sections

Split the piping at every tee. A section is one run of pipe between the point of delivery, a tee, or an appliance outlet. A section that ends at an appliance needs the input rating in Btu per hour as printed on the rating plate, for example 80,000, not 80 MBH. A section that feeds other sections gets its load from them.

3. Method

Length method Longest length method (IFGC 402.4.1). Every section is sized with the longest run from the point of delivery to the most remote outlet. Branch length method (IFGC 402.4.2). Sections on the longest run use the longest run. Every other section uses the length from the point of delivery to the most remote outlet it feeds.

Length handling Round up to the code table rows. Uses the next longer length row of the code tables, the way the table is read. A size is not selected where the code tables print NA (a capacity below 10 cubic feet per hour). Exact length. Uses the length as entered, never less than 10 ft.

Result

Pipe size for each section
Section	Load (cfh)	Sizing length (ft)	Min. inside diameter (in.)	Selected size	Capacity (cfh)

Load is rounded up and capacity is rounded down for display. The selection uses the unrounded numbers. The printed code tables are rounded, so a table value can differ from the computed capacity by up to half a unit of its last printed digit.

Layout as entered
Section	Fed from	Length (ft)	Fittings and valves	Appliance input (Btu/h)

Show the math

Minimum inside diameter, 2024 IFGC Section 402.4, Equation 4-1 (low pressure, less than 1.5 psi):

D = Q to the power ^0.381 ÷ (19.17 × (ΔH ÷ (Cr × L)) to the power ^0.206)

Capacity of a pipe, 2024 IFGC Appendix A, Section A104, low pressure form:

Q = 2,313 × D to the power ^2.623 × (ΔH ÷ (Cr × L)) to the power ^0.541

D is the inside diameter in inches, Q the gas flow in cubic feet per hour, ΔH the pressure drop in inches water column, L the length in feet, and Cr = 0.6094 for natural gas (IFGC Table 402.4). A size is selected where its capacity is at least the load and its inside diameter is at least the Equation 4-1 diameter. More detail is on the methodology page.

What this tool does not do

Corrugated stainless steel tubing (CSST). It is sized from the tubing manufacturer's tables for the product and its EHD size.
Propane (LP gas).
Systems at 1.5 psi and above, 2 psi systems, and regulator selection.
Polyethylene pipe, stainless steel tubing and other materials.
Jobs above 2,000 ft elevation, gas heavier than 0.70 specific gravity, and load diversity factors.
Runs longer than 2,000 ft and pipe larger than 4 in. steel or 2 in. copper.
Appliance connectors, meters, venting, combustion air, testing and purging.

The equations, constants, pipe diameters and sources are on the methodology page. Sources were last checked on October 2, 2026.