Use the free Gas Pipe Size Estimator below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
What this tool does
Gas pipe sizing is one of those jobs where a wrong guess is not just inconvenient: too small a pipe starves appliances of gas, and too large a pipe wastes money and complicates the installation. This educational gas pipe size estimator gives a first estimate from two numbers, the total gas load in BTU per hour and the length of the run in feet, using a simplified capacity table for natural gas. Read the safety warning carefully: this tool teaches the idea, it does not approve an installation, and gas work must always be done by a licensed professional.
Add up the BTU ratings of every appliance on the run: a furnace, a water heater, a cooker, a dryer, and anything else the pipe will feed, using the rating plates rather than guesses. Enter that total and the length of the longest run from the meter or regulator to the furthest appliance, in feet. Press Calculate and the tool picks the table row for the next length above yours, which is the conservative choice, and then the smallest pipe size whose capacity on that row covers your load. If your load is above the largest size shown, the tool says so plainly instead of inventing a size.
The table behind the tool is a simplified version of the kind published in gas codes, for natural gas at a typical pressure drop. On the thirty-foot row, for example, a half-inch pipe carries about seventy-five thousand BTU per hour, a three-quarter-inch pipe about one hundred and sixty thousand, a one-inch pipe about two hundred and seventy thousand, and a two-inch pipe about one point four million. Longer runs carry less on the same size, because friction over distance eats pressure, so a load that fits a small pipe on a short run may need a larger pipe on a long one. That trade-off between load, length, and size is the whole sizing problem in miniature.
Take a home with a furnace at eighty thousand BTU per hour and a water heater at forty thousand, for a total of one hundred and twenty thousand, on a thirty-foot run. The thirty-foot row gives seventy-five thousand for half-inch, which is too small, and one hundred and sixty thousand for three-quarter-inch, which covers the load, so the tool suggests three-quarter-inch. Add a cooker at sixty thousand and the total becomes one hundred and eighty thousand, which needs a one-inch pipe on the same row. Those steps show why adding one appliance later can mean replacing a pipe, not just teeing off it.
Three errors are common and all are dangerous. First, people size only for the appliance they are adding today and forget the others already on the run. Second, they measure the straight distance and forget bends, fittings, and the route the pipe actually takes, which all add effective length. Third, they use the wrong gas: propane, different pressures, and different pressure drops need different tables, and this tool’s table is for natural gas at a typical drop only. If any of those apply, stop and ask a licensed gas fitter, because an online table cannot see your meter pressure, your regulator, or your local code.
Can I install gas pipe myself from this estimate? No: gas installation is licensed work in most places, and it must be tested, inspected, and signed off. Does a bigger pipe hurt? A larger pipe costs more and is harder to route, but it does not starve appliances; the risk of oversizing is cost and practicality, not safety, unlike undersizing. Why does the tool round length up? Because using the next longer table row is the safe, conservative choice when your exact length falls between rows, and a professional will confirm the final size against the full code tables.
Important limits: an estimate, not a code approval
Every result on this page is an educational estimate only. It is not professional advice and it does not guarantee compliance with any building, plumbing, gas, or safety code. Local rules, soil, climate, pipe material, and the condition of an existing system can change the correct answer, and this tool cannot see any of those things. Gas work must be done by a licensed professional and checked against local gas codes; never size, install, or alter gas pipework from an online estimate. For any real installation, repair, or purchase decision, consult a licensed plumber or carpenter first, and get a second opinion when the job is large, expensive, or safety-critical. Use this tool to plan, compare, and ask better questions — not as a substitute for a qualified person on site.
Also available in Spanish: Spanish version.