Low-pressure natural gas
Size Schedule 40 Natural Gas Pipe
Find the first listed pipe size whose unrounded Equation 4-1 capacity meets the connected demand.
Default reference: 100,000 Btu/h at 50 ft equivalent length, 0.5 in. w.c. allowable pressure drop, and 1,000 Btu/ft³ requires about 0.703 in inside diameter; the first qualifying listed size is NPS 3/4 (DN20).
Default calculation shown.
Preliminary model-code calculation
Use maximum appliance input ratings and all applicable simultaneous downstream loads. Determine the correct sizing method and equivalent length, then verify available pressure, allowable pressure drop, utility gas characteristics, adopted code, manufacturer instructions, and the authority having jurisdiction.
Calculated reference
Calculated Natural Gas Capacity by Pipe Size and Equivalent Length
0.5 in. w.c. allowable pressure drop · capacity in CFH
The first row follows the exact selected length when JavaScript is available. Standard reference rows remain below it. Scroll within the table on smaller screens.
Scroll horizontally to view additional pipe sizes and vertically to view additional lengths. Column headers and the equivalent-length column remain visible while scrolling.
| Maximum calculated capacity, CFH | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| NPS 1/2 DN15 · ID 0.622 in | NPS 3/4 DN20 · ID 0.824 in | NPS 1 DN25 · ID 1.049 in | NPS 1-1/4 DN32 · ID 1.380 in | NPS 1-1/2 DN40 · ID 1.610 in | NPS 2 DN50 · ID 2.067 in | NPS 2-1/2 DN65 · ID 2.469 in | NPS 3 DN80 · ID 3.068 in | NPS 4 DN100 · ID 4.026 in | |
| Selected — 50 ft | 72.5 | 152 | 286 | 587 | 880 | 1,695 | 2,702 | 4,778 | 9,750 |
| 10 ft | 173 | 362 | 682 | 1,401 | 2,100 | 4,046 | 6,450 | 11,407 | 23,276 |
| 20 ft | 119 | 249 | 469 | 963 | 1,443 | 2,781 | 4,434 | 7,841 | 16,001 |
| 30 ft | 95.5 | 200 | 377 | 774 | 1,159 | 2,234 | 3,561 | 6,298 | 12,851 |
| 40 ft | 81.8 | 171 | 322 | 662 | 992 | 1,912 | 3,048 | 5,391 | 11,000 |
| 50 ft | 72.5 | 152 | 286 | 587 | 880 | 1,695 | 2,702 | 4,778 | 9,750 |
| 60 ft | 65.7 | 137 | 259 | 532 | 797 | 1,536 | 2,448 | 4,329 | 8,834 |
| 75 ft | 58.2 | 122 | 229 | 471 | 706 | 1,361 | 2,170 | 3,837 | 7,830 |
| 100 ft | 49.8 | 104 | 196 | 403 | 605 | 1,165 | 1,857 | 3,285 | 6,702 |
| 125 ft | 44.2 | 92.4 | 174 | 358 | 536 | 1,033 | 1,646 | 2,911 | 5,941 |
| 150 ft | 40.0 | 83.7 | 158 | 324 | 486 | 936 | 1,492 | 2,638 | 5,383 |
| 200 ft | 34.2 | 71.6 | 135 | 277 | 416 | 801 | 1,277 | 2,258 | 4,608 |
| 250 ft | 30.4 | 63.5 | 120 | 246 | 368 | 710 | 1,132 | 2,001 | 4,084 |
| 300 ft | 27.5 | 57.5 | 108 | 223 | 334 | 643 | 1,025 | 1,813 | 3,700 |
| 400 ft | 23.5 | 49.3 | 92.8 | 191 | 286 | 551 | 878 | 1,552 | 3,167 |
| 500 ft | 20.9 | 43.7 | 82.3 | 169 | 253 | 488 | 778 | 1,376 | 2,807 |
Capacities are displayed to about three significant figures. Qualification uses unrounded values. CFH is not automatically equal to MBH unless the entered heating value is exactly 1,000 Btu/ft³.
No Schedule 40 size from NPS 1/2 through 4 qualifies within this page’s verified scope. Use the adopted fuel-gas code, utility requirements, and an engineered or higher-pressure design; do not extrapolate this chart.
How to Use the Natural Gas Pipe Sizing Chart
- Total the connected input load. Use appliance maximum input ratings, not output ratings, and include simultaneous downstream loads that apply to the segment being sized.
- Determine the applicable equivalent length. Use the length required by the adopted longest-length, branch-length, or other permitted sizing procedure.
- Confirm allowable pressure drop. The default is 0.5 in. w.c.; 0.3 in. w.c. and a bounded custom value are also available.
- Use the utility heating value when known. Energy-rate inputs are converted to CFH from the entered gas heat content.
- Read the first qualifying size. The result compares the required inside diameter with the limited Schedule 40 size set and shows the smaller-size shortfall and next-size headroom.
Selection rule: the smallest listed pipe whose unrounded calculated capacity is greater than or equal to the unrounded required flow is selected.
Longest-Length and Branch-Length Sizing Methods
Longest-length approach
Identify the governing run from the point of delivery to the most remote outlet, then apply the code-prescribed method to the applicable system sections. This is intentionally conservative in many layouts and is commonly used because it is straightforward to apply.
Branch-length approach
Some permitted sizing procedures use the length associated with each branch or section rather than one system-wide governing length. Use this only when the adopted code and project method allow it.
The calculator does not decide which method is permitted for a specific installation. Establish that method first, then enter the resulting equivalent length.
Assumptions Behind the Calculated Capacities
- Fuel
- Natural gas only; fixed Equation 4-1 natural-gas factor Cr = 0.6094.
- Pressure regime
- Low-pressure Equation 4-1 scope only; elevated-pressure distribution is excluded.
- Flow reference
- CFH is referenced to 60°F and a 30-inch mercury column, matching the IFGC Equation 4-1 definition of Q.
- Pipe basis
- Limited Schedule 40 steel-pipe inside diameters from NPS 1/2 through NPS 4.
- Length range
- 10–500 ft equivalent. The tool refuses to extrapolate outside this range.
- Pressure-drop range
- 0.1–1.0 in. w.c. equivalent. Common presets are 0.3 and 0.5 in. w.c.
- Heating-value range
- 800–1,200 Btu/ft³ equivalent; utility-specific data should be used when available.
Equation used
Required inside diameter:
D is inside diameter in inches, Q is required flow in CFH, ΔH is allowable pressure drop in inches of water column, L is equivalent length in feet, and Cr is 0.6094 for natural gas.
Capacity form
For each listed inside diameter, the equation is rearranged to calculate Q. The page then compares the unrounded pipe capacity with the unrounded required flow.
Worked Natural Gas Pipe Sizing Examples
Example 1: 100,000 Btu/h at 50 ft
Assumptions: 1,000 Btu/ft³ natural gas and 0.5 in. w.c. allowable pressure drop.
Required flow = 100,000 ÷ 1,000 = 100 CFH. Equation 4-1 gives a required ID of about 0.703 in.
NPS 1/2 (0.622 in ID) calculates to about 72.5 CFH and is insufficient. NPS 3/4 (0.824 in ID) calculates to about 152 CFH, so it is the first qualifying listed size.
Sanity check: the next larger NPS 1 size has substantially more capacity; do not use that extra margin as a substitute for confirming the governing pressure and length method.
Example 2: 250,000 Btu/h at 100 ft
Assumptions: 1,000 Btu/ft³ natural gas and 0.5 in. w.c. allowable pressure drop.
Required flow = 250 CFH. Equation 4-1 gives a required ID of about 1.150 in.
NPS 1 (1.049 in ID) calculates to about 196 CFH and is insufficient. NPS 1-1/4 (1.380 in ID) calculates to about 403 CFH and is the first qualifying listed size.
Sanity check: this result applies only to the stated low-pressure natural-gas basis and the limited Schedule 40 size set.
Common Natural Gas Pipe Sizing Mistakes
- Using appliance output instead of input. Fuel-gas sizing is based on the appliance input rating.
- Omitting simultaneous downstream loads. A segment can carry more than the load of the single appliance nearest it.
- Using straight-line distance. Enter the length required by the applicable sizing method, including fittings or equivalent length when that method requires them.
- Assuming every cubic foot contains exactly 1,000 Btu. Actual utility heat content varies; use the supplied local value when available.
- Confusing nominal pipe size with actual inside diameter. The equation uses actual inside diameter, not the nominal NPS label.
- Mixing fuels, materials, schedules, or pressure systems. Those changes can invalidate both the dimensions and the governing method.
Schedule 40, CSST, PE, Copper, Propane, and 2-psi Systems Are Separate
Covered on this page
- Natural gas
- Low-pressure Equation 4-1 basis
- Schedule 40 steel-pipe dimensional set
- NPS 1/2 through NPS 4
- 10–500 ft equivalent length
Requires another method or source
- Propane/LP gas
- CSST or manufacturer-specific tubing
- Polyethylene or copper tubing
- Other pipe schedules
- Elevated-pressure or 2-psi distribution systems
- Meter, regulator, and complete network design
Do not reinterpret this result for another fuel or piping system. Different dimensions, coefficients, regulator arrangements, manufacturer data, and adopted-code provisions can govern.
Sources, Edition, Method, and Data Rights
Calculated low-pressure natural-gas capacities for a limited Schedule 40 steel-pipe dimensional set; no ICC or ASME standards table is reproduced.
The hydraulic calculation uses one controlling formulation: 2024 IFGC Section 402.4, Equation 4-1. ICC CodeNotes supplies method context, the limited pipe inside diameters are dimensional inputs, and EIA supplies heat-content context.
- International Code Council — 2024 International Fuel Gas Code, Chapter 4Section 402.4, Equation 4-1 and the natural-gas equation factor are the calculation basis used here.
- ICC CodeNotes — Fuel Gas Pipe SizingUsed for method context such as appliance input, simultaneous connected load, longest-length, and branch-length sizing.
- ASME B36.10-2022 — Welded and Seamless Wrought Steel PipeDimensional basis for the limited Schedule 40 pipe sizes used as equation inputs; no ASME table is reproduced here.
- U.S. Energy Information Administration — Natural Gas Heat ContentUsed to explain why actual gas heating value varies and why utility-provided heat content is preferable when available.
Dataset and Source-Check Details
- Dataset label
- NG-SCH40-IFGC2024-EQ4-1-v1.0
- Equation basis
- 2024 IFGC Section 402.4, Equation 4-1
- Natural-gas factor
- Cr = 0.6094
- Flow reference conditions
- Q in CFH at 60°F and 30 in. Hg, per the IFGC Equation 4-1 variable definition
- Pipe dimensional basis
- Limited ASME B36.10-2022-based Turn2Engineering Pipe Size Reference 1.0 values
- Valid page range
- 1–10,000 CFH; 10–500 ft; 0.1–1.0 in. w.c.; 800–1,200 Btu/ft³
- Rights decision
- Original calculations and limited dimensional facts only; no full standards-table reproduction or bulk CSV
- Publisher
- Turn2Engineering
- Source check
- Source checked August 6, 2026; this is not an engineering approval or jurisdictional code review
Natural Gas Pipe Sizing FAQ
It depends on equivalent length, allowable pressure drop, and gas heating value. With this page’s defaults of 50 ft, 0.5 in. w.c., and 1,000 Btu/ft³, the calculation selects NPS 3/4 from the limited Schedule 40 size set.
No. A 1,000 Btu/ft³ value is a convenient convention, but actual gas heat content varies by location and time. Use the local utility value when available.
Use the equivalent-length or sizing procedure required by the adopted code or applicable manufacturer method rather than applying a universal percentage or fixed allowance.
No. Those systems use different dimensional, fuel, pressure, code, or manufacturer-specific data and require a separate sizing method.
Yes. Adopted editions, amendments, available pressure, allowable pressure drop, utility requirements, altitude, regulator arrangement, and equipment instructions can change the governing design.
Natural Gas Pipe Sizing Summary
Before using a preliminary size for design or installation, confirm these six items:
- Maximum connected appliance input and simultaneous downstream load
- Applicable longest-length, branch-length, or equivalent-length method
- Available gas pressure and allowable pressure drop
- Correct fuel, pipe material, schedule, and inside diameter
- Utility gas heating value and project-specific requirements
- Adopted code, manufacturer instructions, and authority having jurisdiction