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Fire Pit Gas Line Sizing Calculator

Enter the fuel, total load, run length and pipe material. The result is the smallest pipe size that carries the load within the International Fuel Gas Code's 0.5 in. w.c. pressure drop, plus the next size up.

Inputs

Propane means undiluted propane after the second-stage regulator, at 11.0 in. w.c.

Add up the rated input of every appliance on the run.

From the meter or regulator to the farthest appliance. If the run has four or more fittings, add their equivalent length.

CSST and copper are not covered. Size CSST from its manufacturer's tables.

Result

Smallest Schedule 40 metallic pipe for this load

1/2 in.

Pipe
1/2 in. Schedule 40 metallic
Next size up
3/4 in.
Gas flow
65.0 cu ft per hour
Inside diameter required by Equation 4-1
0.597 in.
Inside diameter of the selected size
0.622 in.
Capacity of the selected size after the 2.5% reduction
70,659 Btu/h
Share of that capacity your load uses
92%

Notes on This Result

  • Your load is above 90% of what a 1/2 in. line carries once the 2.5% reduction is applied. The code tables may call for the next size up, and your installer sizes to the code edition your jurisdiction adopted.
  • This is a sizing check, not an installation plan. Your installer sizes from the code edition your jurisdiction adopted, tests the system for leaks before it is put in service or covered, and pulls whatever permit applies locally. Your appliance manual may call for a larger pipe than the code table, and your installer works to both.
  • The equation only guarantees a 0.5 in. w.c. pressure drop. Whether the burner gets enough pressure depends on the supply pressure and the appliance's own minimum inlet pressure, which is in its manual. Utility supply pressure varies.
  • If your run has four or more fittings, add their equivalent length to the length you enter (IFGC Appendix A, A102.2). A screwed 90 degree elbow adds 1.55 ft in 1/2 in. pipe, 2.06 ft in 3/4 in. pipe, 2.62 ft in 1 in. pipe, 3.45 ft in 1-1/4 in. pipe.
  • Above 2,000 feet elevation the code requires the flow to be adjusted for altitude. This tool does not model that.

Calculation Details

Formula

D = Q^0.381 / (19.17 × (ΔH / (Cr × L))^0.206), with Q = load ÷ heating value and ΔH = 0.5 in. w.c. Each size's capacity is reduced by 2.5% before it is chosen. Source: International Fuel Gas Code, Equation 4-1 (Section 402.4) and Table 402.4.

Assumptions

  • This uses the low-pressure sizing equation from the International Fuel Gas Code (Equation 4-1), for systems under 1-1/2 psi.
  • Allowable pressure drop is 0.5 inch water column, the basis of the code's standard low-pressure tables.
  • Natural gas is taken at 1,000 Btu per cubic foot and a specific gravity of 0.60. Your gas utility can give you the local heating value.
  • The load is the full rated input of everything on the run, all burning at once.
  • Length is the run from the meter or regulator to the farthest appliance. If your run has four or more fittings, add their equivalent length before you enter it.
  • Each size's capacity is reduced by 2.5% before it is chosen, because the equation can read up to about 2.4% above the code's printed tables. That keeps this tool from being more permissive than the tables.
  • Schedule 40 metallic pipe and polyethylene only. Polyethylene is for outdoor underground runs. CSST is not sized here: it is sized from its manufacturer's tables by equivalent hydraulic diameter, not by a nominal pipe size, so a generic equation cannot stand in for a specific product's listing. Copper tubing is not covered.
  • This sizes one straight run. It does not size a branched system, a higher-pressure system, or the pipe upstream of a regulator.
  • The page cites the International Fuel Gas Code, 2027 edition. The equation and table values are unchanged from the 2024 edition most jurisdictions have adopted. NFPA 54, the National Fuel Gas Code, is the companion national standard and is not quoted here.

Sources

  1. ICC, International Fuel Gas Code 2027 Version 1.0 (Aug 2026), Chapter 4. Equation, Cr values and table values are identical in the 2024 IFGC Version 2.0; only the table numbers differ, Section 402.4 Equation 4-1 (low-pressure gas, less than 1-1/2 psi), coefficient

    Checked . View at codes.iccsafe.org.

  2. ICC, International Fuel Gas Code 2027 Version 1.0 (Aug 2026), Chapter 4. Equation, Cr values and table values are identical in the 2024 IFGC Version 2.0; only the table numbers differ, Section 402.4 Equation 4-1, exponent on Q

    Checked . View at codes.iccsafe.org.

  3. ICC, International Fuel Gas Code 2027 Version 1.0 (Aug 2026), Chapter 4. Equation, Cr values and table values are identical in the 2024 IFGC Version 2.0; only the table numbers differ, Section 402.4 Equation 4-1, exponent on the pressure drop term

    Checked . View at codes.iccsafe.org.

  4. ICC, International Fuel Gas Code 2027 Version 1.0 (Aug 2026), Chapter 4. Equation, Cr values and table values are identical in the 2024 IFGC Version 2.0; only the table numbers differ, Table 402.4 'Cr and Y values for natural gas and undiluted propane at standard conditions', natural gas (specific gravity 0.60)

    Checked . View at codes.iccsafe.org.

  5. ICC, IFGC 2027 Appendix A (informative), A102.2 and A102.3: Tables 402.4(2), 402.4(8), 402.4(12), 402.4(18) and the propane tables are based on a pressure drop of 0.5 in. w.c. Section 402.6 sets only a performance rule

    Checked . View at codes.iccsafe.org.

  6. ICC, IFGC 2027 Appendix A, A106.1 Example 1: natural gas of 0.60 specific gravity and a heating value of 1,000 Btu/ft3. Your gas supplier gives the local value (A102.1). Cross-check: U.S. EIA sample factor 1 cubic foot = 1,036 Btu, so 1,000 errs toward the larger pipe (https://www.eia.gov/energyexplained/units-and-calculators/)

    Checked . View at codes.iccsafe.org.

  7. ICC, International Fuel Gas Code 2027 Version 1.0 (Aug 2026), Chapter 4. Equation, Cr values and table values are identical in the 2024 IFGC Version 2.0; only the table numbers differ, Table 402.4(2) 'Actual ID' row (Schedule 40 metallic). All nine sizes appear in the natural gas and propane tables, so one list serves both fuels

    Checked . View at codes.iccsafe.org.

  8. Firepit HQ DECISIONS D59, derived from the dossier comparison of Equation 4-1 against IFGC Tables 402.4(2), 402.4(18), 402.4(25) and 402.4(32): the equation reads from 0.72% below to 2.37% above the printed table values

    Checked .

  9. ICC, IFGC 2027 Appendix A, A102.2: an allowance (in equivalent length of pipe) should be considered for any piping run with four or more fittings (see Table A102.2)

    Checked . View at codes.iccsafe.org.

  10. ICC, IFGC 2027 Section 402.2: flow shall be adjusted for altitude where the installation is above 2,000 feet

    Checked . View at codes.iccsafe.org.

What the Result Means

The result is the smallest nominal pipe size whose capacity, after a 2.5% reduction, covers your load over your run. The reduction keeps the tool from being more permissive than the code's printed tables, because the equation can read up to about 2.4% above them. When your load uses more than 90% of the chosen size, the tool says so. Treat that as a reason to ask your installer about the next size up.

The load is the full rated input of everything on the run, all burning at once. A pipe that feeds one fire table comfortably may be too small once a patio heater is added to the same line.

The equation holds the pressure drop to 0.5 in. w.c., and that is all it checks. Whether your burner gets enough pressure depends on the supply pressure and the appliance's own minimum inlet pressure, which is printed in its manual. Real Flame's Baltic 9750NG manual, for example, gives a minimum inlet pressure of 3.5 in. w.c. for natural gas. Four or more fittings call for an equivalent-length allowance, so add it to the length before you enter it. Above 2,000 feet of elevation the code requires the flow to be adjusted, and this tool does not do that.

The tool sizes one straight run. It does not cover branched systems, higher-pressure systems or the pipe upstream of a regulator. CSST is left out on purpose. It is sized from its manufacturer's tables by equivalent hydraulic diameter rather than by nominal size, and a generic equation cannot stand in for a specific product's listing.

Hire a licensed installer for the actual installation. They size from the code edition your jurisdiction adopted, test the system for leaks before it is put in service or concealed, and pull whatever permit applies. Polyethylene is for outdoor underground runs only, with its own burial depth and tracer wire rules.

Related Calculators

Your state or city decides which fuel gas code applies and which edition. Our state code pages list what we have verified for each state, including its gas appliance rules. See Fire Codes by State.

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