Fuel-gas capacity

Gas Line Sizing Calculator

Use this gas line sizing calculator to find the minimum nominal Schedule 40 metallic-pipe size for a natural-gas segment. Enter its downstream appliance load and the system’s longest design length to select the appropriate table capacity.

Table-based sizing

Size a Natural-Gas Line

1 Enter the segment conditions

Longest design length

Measure from the meter or point of delivery to the most remote outlet. Include any required fitting allowance in this design length.

Connected appliance input

Btu/h

Add the maximum input ratings for all appliances supplied downstream of this segment, or build the total from individual appliances below.

Natural-gas heating value

Btu/ft³

Use the value from the gas utility when known. 1,000 Btu/ft³ is a common planning value.

Sizing table

Schedule 40 metallic pipe
Natural gas, 0.60 specific gravity, under 2 psi inlet pressure, with a 0.5 in. w.c. pressure drop.

Existing or planned nominal pipe size Optional

Checks this size against the calculated demand at the selected table row. It does not verify an installed system.

Build the load from individual appliances Optional

Add every appliance supplied downstream of this segment. Common planning presets can speed up entry, but replace them with the actual maximum nameplate input before sizing. A completed list updates the connected-input total above.

No appliance rows added. Enter a total load above.

Calculated result

Minimum Nominal Pipe Size

Table-based minimum

—

Connected load—maximum downstream input

Gas demand—input ÷ heating value

Length row used—next longer table row

Selected capacity—capacity at the table row

Next size up—next listed pipe size

Before installationUse the adopted local fuel-gas code, utility requirements, approved material-specific tables, and a qualified installer or designer to confirm the system. This result does not establish code compliance or installation safety.

Show the calculation method

Capacity comparison
Nominal pipe size	Capacity	Equivalent appliance input

Use the right load

How This Gas Line Sizing Calculator Works

Add downstream demand

Use the maximum input rating from every appliance supplied by the pipe segment, assuming simultaneous operation.

Choose the longest row

Enter the longest design length from the point of delivery to the most remote outlet. The calculator rounds up to the next table row.

Select adequate capacity

The first pipe size whose table capacity meets or exceeds the calculated cubic-feet-per-hour demand is returned.

Worked example

Size a 100,000 Btu/h Gas-Pipe Segment

Suppose a pipe segment supplies 100,000 Btu/h of connected appliance input. The longest design length from the point of delivery to the most remote outlet is 50 feet, and the available natural-gas heating value is 1,000 Btu/ft³.

A gas meter feeds one dark steel pipe with teal flow arrows toward a gas appliance. A dimension line follows the pipe route and a magnified pipe end highlights the nominal pipe size. — Check one pipe segment by using its downstream demand and the system’s longest design length.

01
Find gas demand: 100,000 Btu/h ÷ 1,000 Btu/ft³ = 100 CFH.
02
Use the 50-foot row: The longest design length matches the 50-foot table row, so that row is used for this segment.
03
Choose the first adequate size: At 50 feet, ½ in. pipe is listed at 72 CFH and is too small. The next size, ¾ in., is listed at 151 CFH, so the table-based minimum is ¾ in.

This is an example of the calculator’s table-based result, not an installation design. Confirm the actual appliance inputs, delivery conditions, adopted code, and pipe material before work begins.

For a full system

How to Size Multiple Gas-Pipe Segments

With the longest-length method, first find one design length from the meter or other point of delivery to the most remote outlet. Use that equal or next-longer table row when checking every Schedule 40 metallic-pipe segment in the system.

A gas meter feeds a large main pipe that splits into two branch pipes, one serving a wall-mounted appliance and the other serving a range. Teal arrows show gas flow, and a dashed dimension line runs to the most remote appliance. — The main carries the combined downstream demand. Each branch carries the demand of the appliance or appliances it serves.

Then calculate each segment’s own downstream demand. A main that supplies several appliances carries the combined load of all of them. A branch carries only the load of the appliances beyond that branch. Enter each known segment load separately in this calculator to check its table-based minimum size.

This calculator does not draw a piping diagram or decide which appliances are downstream of each segment. Use the plans and actual pipe layout to identify those loads before calculating.

Scope and limits

What This Calculator Does and Does Not Size

This calculator handles one natural-gas Schedule 40 metallic-pipe segment using the longest-length method and table rows from 10 through 350 feet. It does not size propane, CSST, copper, polyethylene, higher-pressure systems, gas meters, regulators, combustion air, venting, appliance connectors, branches from a piping diagram, or pipe installation details.

For every gas-pipe project, confirm the current locally adopted code and the gas utility’s delivery conditions. The ICC fuel-gas pipe sizing notes explain the longest-length method and its table selection process.

Quick answers

Gas Line Sizing FAQs

What length should I enter?

Enter the longest design length from the meter or other point of delivery to the most remote outlet in the system, including any applicable equivalent length for fittings. This same table row is used when sizing each section by the longest-length method.

How do I find the appliance load?

Use each appliance’s maximum input rating from its nameplate or manufacturer literature. Add the loads of every appliance that the pipe segment supplies; do not use an appliance’s output rating.

How do I size a main and a branch?

Use the same longest-length table row for both, then enter the downstream load carried by each segment. The main carries the combined demand of the appliances it supplies; a branch carries only the demand beyond that branch.

Does the existing-pipe check confirm my installation?

No. It compares the selected nominal size with this calculator’s listed capacity at the chosen table row. Confirm pipe material, actual route length, fittings, fuel conditions, code requirements, and the installed system separately.

Can I use this for propane or CSST?

No. Propane, CSST, copper tubing, polyethylene, and other materials or pressure conditions use different capacity tables. Use the table specified for the actual fuel, material, pressure, and local code.

Why does the calculator round the length up?

The longest-length method uses the table row equal to the measured length or the next longer row when there is no exact match. This is more conservative than rounding down.