TradesHow this works
Natural gas pipe is sized so every appliance gets enough gas at once without the pressure dropping too far. You add up the BTU of all the appliances, convert that to cubic feet per hour, and find the pipe that carries it over your longest run. Longer runs and bigger loads need bigger pipe. This tool runs that lookup from the NFPA 54 table for standard low-pressure systems in Schedule 40 steel.
It uses the longest-length method: it sizes for the run from the meter to the farthest appliance. That is the conservative, code-recognized approach for a simple system. It is a starting point and a sanity check, not a design, and it is natural gas only.
Common questions
Should I really size my own gas line?
Use this to understand the ballpark and check a plan, not to run pipe. Gas work is dangerous and is regulated. It should be sized, installed, and inspected by a licensed professional to the code and the appliance nameplates in your area.
What is the longest-length method?
It is the standard NFPA 54 approach for simple systems. You find the longest run from the meter to the farthest appliance, then size every section of pipe using that one length. It is conservative and easy to follow.
How do I get the BTU load?
Add up the input rating on every gas appliance nameplate. A furnace is often 60,000 to 100,000 BTU, a tankless water heater up to about 199,000, a tank heater around 40,000, a range around 65,000, a dryer around 35,000. Use the actual nameplate, not these rough numbers.
Does this work for propane?
No. This is natural gas only, at standard low pressure under 2 psi, in Schedule 40 steel pipe. Propane, CSST tubing, and 2 psi systems use different tables.
Sources: IFGC Table 402.4(2) / NFPA 54 Table 6.2(a) — Schedule 40, natural gas, 0.60 SG, <2 psi, 0.5 in w.c. (2021). Engine version 1.0.0. Risk tier 2.