Gas Line Pipe Size Calculator
Convert gas line pipe diameter to maximum BTU delivery capacity based on pipe length and gas pressure.
Covers natural gas and propane systems.
Enter the pipe run length and total BTU demand to determine the correct gas line size.
Understanding Gas Line Sizing
Gas line pipe diameter determines the maximum amount of gas (measured in BTU per hour) that can flow to your appliances. An undersized gas line causes low gas pressure at the appliance, resulting in reduced performance, pilot light problems, and incomplete combustion that produces dangerous carbon monoxide. Gas lines must be sized to deliver the total BTU demand of all connected appliances with adequate pressure at the furthest point.
Natural Gas Pipe Capacity (0.5 PSI system, less than 0.5 in WC pressure drop):
| Pipe Size | 10 ft (3 m) | 20 ft (6 m) | 50 ft (15 m) | 100 ft (30 m) | 200 ft (61 m) |
|---|---|---|---|---|---|
| 1/2 in (15 mm) | 175,000 | 120,000 | 75,000 | 52,000 | 35,000 |
| 3/4 in (20 mm) | 360,000 | 250,000 | 152,000 | 106,000 | 73,000 |
| 1 in (25 mm) | 680,000 | 465,000 | 285,000 | 199,000 | 138,000 |
| 1-1/4 in (32 mm) | 1,400,000 | 950,000 | 580,000 | 400,000 | 280,000 |
| 1-1/2 in (40 mm) | 2,100,000 | 1,460,000 | 890,000 | 620,000 | 430,000 |
| 2 in (50 mm) | 3,950,000 | 2,750,000 | 1,670,000 | 1,170,000 | 810,000 |
All values are in BTU per hour for natural gas at standard conditions.
Propane (LP Gas) Adjustment:
Propane delivers approximately 2,516 BTU per cubic foot compared to 1,030 BTU per cubic foot for natural gas. However, propane systems typically operate at higher pressure (11 inches water column versus 7 inches for natural gas). When using the table above for propane, multiply the BTU capacity by 1.5 as a general approximation. Always consult local codes for exact propane pipe sizing requirements, as they differ from natural gas.
Common Appliance BTU Demands:
| Appliance | BTU Input | Pipe Size (50 ft run) |
|---|---|---|
| Gas range / oven | 60,000 - 90,000 | 1/2 in (15 mm) |
| Tankless water heater | 150,000 - 200,000 | 3/4 in (20 mm) |
| Tank water heater (40 gal) | 35,000 - 40,000 | 1/2 in (15 mm) |
| Furnace (80,000 BTU) | 80,000 | 1/2 in (15 mm) |
| Furnace (120,000 BTU) | 120,000 | 3/4 in (20 mm) |
| Gas fireplace | 25,000 - 40,000 | 1/2 in (15 mm) |
| Gas dryer | 22,000 - 25,000 | 1/2 in (15 mm) |
| Pool heater | 200,000 - 400,000 | 3/4 - 1 in (20 - 25 mm) |
| Whole-house generator | 150,000 - 300,000 | 3/4 - 1 in (20 - 25 mm) |
Sizing the Main Line:
The main gas line from the meter to the house must be large enough to supply the total combined BTU demand of all appliances that could operate simultaneously. Add up the BTU input ratings of all gas appliances, then use the pipe capacity table for the total length of the main line from the meter to the first branch point. Each branch line is then sized for the specific appliance or group of appliances it serves.
Equivalent Length for Fittings:
Each pipe fitting adds resistance equivalent to additional straight pipe. A standard 90-degree elbow adds approximately 2 to 5 feet (0.6 to 1.5 meters) of equivalent length depending on pipe size. A tee fitting adds 3 to 7 feet (0.9 to 2.1 meters). Add these equivalent lengths to the actual pipe length when using the sizing table.
Pressure Testing:
After installation, all gas lines must be pressure tested before being put into service. The standard test is 3 PSI (21 kPa) of air pressure held for 15 minutes with no measurable drop. Never use an open flame to test for leaks. Use a soap-and-water solution or an electronic gas detector.
Safety Note:
Gas line installation and modification should only be performed by licensed plumbers or gas fitters. Improper installation can cause gas leaks, fires, explosions, and carbon monoxide poisoning. Always obtain the required permits and inspections for gas line work.