Gas Network Sizing & Capacity Verification
How to use this tool (click to expand instructions)
- Click any junction letter (A, B, C…) to add a new pipe section or appliance from that point, or to remove that junction and everything connected to it.
- Enter the pipe length and diameter for each section, and the BTU/hr rating for each appliance.
- Pipe sections and appliance boxes turn green when adequate, and red when the pressure drop exceeds your allowable limit.
- If a pipe run includes fittings (elbows, tees, valves), convert them to an equivalent length using the “Equiv. Length Calc” link at the bottom left, then enter the combined total in the Length field.
- Once every section shows green (OK), click “Download Full Report” at the bottom right to get your formatted calculation for your records or permit submission.
- If a section turns red, the pipe is too small for its current load. Select a larger diameter from that section’s dropdown, or review the appliance loads on that branch, until it turns green.
- The Gas, Inlet Pressure, Allowable Drop, and Meter dropdowns at the top set your project’s basic parameters — adjust them before checking your pipe sizes.
Understanding Gas Pipe Sizing for Your Home or Project
This gas pipe sizing calculator determines the minimum pipe diameter needed to deliver enough fuel gas — natural gas or propane — to every appliance on your system without excessive pressure loss. Undersized pipe causes weak flames, poor appliance performance, and can trigger safety shutoffs; oversized pipe wastes material and installation cost. Most residential systems are designed to a maximum pressure drop of 0.5 inches water column from the meter to the farthest appliance, per NFPA 54, the National Fuel Gas Code used throughout the United States.
Built by a process engineer with 27 years of oil & gas and process design experience. This calculator handles complete branching networks — not just a single pipe run. Click any junction to add trunk lines, branches, and appliances to match your system, and the tool checks pressure drop across every possible path simultaneously, flagging any undersized section in red. It also checks whether your total system load exceeds your gas meter’s rated capacity, a step many simple calculators skip entirely. This tool covers pipe sizes 1/2″ to 2″ for natural gas or propane. For larger pipe, other fluids, or custom fluid properties, use our general Pipe Pressure Drop Calculator instead.
Frequently Asked Questions
Do I need a gas pipe sizing calculation for a permit?
Most building departments require a gas pipe sizing calculation for permit applications, especially when adding a large appliance like a generator, tankless water heater, or pool heater. Check with your local Authority Having Jurisdiction for specific requirements.
What size gas line do I need for a generator?
Standby generators typically require 150,000 to 350,000 BTU/hr, which often exceeds what an existing residential gas line was sized for. Use this calculator to check whether your existing trunk line can handle the added load, or if it needs to be upsized.
Can my existing gas line handle a tankless water heater?
Tankless water heaters use 3 to 5 times more gas than a tank water heater. Enter your existing pipe sizes and lengths along with the new tankless unit’s BTU rating to see if your system is still adequate.
What is the difference between low pressure and 2 PSI gas systems?
Low pressure systems (under 1 PSI) are standard for most homes. Medium pressure (2 PSI) systems use smaller pipe for the same load but require a pressure regulator at each appliance or group of appliances.