BTU calculator for natural gas and propane lines.
Find out what size gas line you need. Add the appliances the line will feed, enter the length of the run, and choose natural gas or propane and the pipe type. The calculator recommends the smallest black steel, polyethylene or CSST pipe that carries the load. Already have a pipe in place? Switch to “How much can my pipe carry?” to see its BTU rating.
Measure from the gas meter (or the propane regulator) to the farthest appliance. Each elbow, tee or union adds about 5 feet. Enter appliance ratings in thousands, so 35 means 35,000 BTU/hr. BTU numbers are typical, so use the rating on your appliance label if you have it.
| Pipe size | Max BTU/hr | Enough? |
|---|
How to use the gas pipe sizing calculator
- Add your appliances. Pick each appliance on the line. The BTU numbers are typical, so use the rating on the appliance label when you have it.
- Measure the run. Measure the gas line from the meter, or from the propane regulator, to the farthest appliance on the line.
- Count the fittings. Every elbow, tee and union slows the gas about as much as 5 more feet of pipe, so the calculator adds 5 feet for each one you enter.
- Pick the pipe type. Black steel is the standard for most gas lines, polyethylene is for buried runs, and CSST is flexible tubing that snakes through walls and floors.
- Read the result. The calculator shows the smallest pipe that works and marks every size as enough or too small.
Where the numbers come from
Every number comes from the sizing tables in the 2021 International Fuel Gas Code: Tables 402.4(2), 402.4(15) and 402.4(21) for natural gas under 2 psi, and Tables 402.4(28), 402.4(32) and 402.4(35) for propane at 11″ water column after the regulator, all with a 0.5″ water column pressure drop. When your length falls between two rows, the calculator follows the table’s own curve between them, so a length that is in the table always returns the table number exactly.
Results are in BTU per hour. One cubic foot of natural gas carries about 1,000 BTU, and one cubic foot of propane carries about 2,516 BTU. CSST ratings vary by brand, so the calculator uses the smaller flow size (EHD) for each nominal size.
Use it as a guide, not a final design
The calculator sizes one line carrying the total load over its full length, which is a simple and conservative method. It does not check branch lines, the actual pressure at your meter, or a specific CSST brand’s chart. Gas work in Washington needs a licensed gas contractor and a permit. Our gas line installation crew sizes the line for your appliances, runs it, pulls the permit and pressure tests it. Planning a fire feature too? See our fire pit installation and gas fireplace installation pages.
Need a gas line for a fire pit or fireplace?
We size it, run it, pull the permit and pressure test it. Free estimates across the Eastside.