Gas Line Size Calculator for Fire Pits and Patio Heaters
Most gas line sizing guides are written for plumbers adding a furnace or range. An outdoor fire pit is a different problem: longer runs, higher BTU loads, and an existing household system that may already be near capacity.
This gas line size calculator covers the full calculation: BTU load to cubic feet per hour, developed length with fitting allowances, and the correct pipe diameter from the NFPA 54 sizing table.
Gas Line Size Calculator
Get the correct pipe diameter for your natural gas fire pit, fire table, or patio heater
Primary Appliance
Found on spec sheet or product label
Second Appliance
Pipe Run
Straight-line distance from meter to appliance
50% is standard for typical outdoor runs
Existing Pipe Check (optional)
Check if tapping an existing line
Sum of all appliances already on this line
Minimum Recommended Pipe Size
—
Schedule 40 black iron pipe — NFPA 54
Total BTU Load
—
BTU/hr
CFH Required
—
cubic feet per hour
Developed Length
—
feet
Spare Capacity
—
BTU/hr headroom
All Pipe Sizes at Your Developed Length
Calculation Breakdown
Appliance BTU (primary)—
Appliance BTU (second)—
Total BTU load—
CFH required (BTU ÷ 1,000)—
Measured pipe length—
Fitting allowance—
Developed length—
NFPA 54 table usedTable 402.4(2) — 0.5" WC
Results based on NFPA 54 Table 402.4(2) for Schedule 40 black iron pipe at standard residential pressure (0.5" WC drop, 7" WC inlet, natural gas 0.60 SG). Always confirm sizing with a licensed gas fitter before installation. Gas line connections require a licensed contractor and permit inspection in all U.S. jurisdictions.
How the Gas Line Size Calculator Works
Step 1: Convert BTU to CFH. Divide the total BTU load by 1,000. A 65,000 BTU fire table requires 65 CFH. Add all appliances that may run simultaneously if this is a shared line.
Step 2: Calculate developed length. Measure the actual pipe run from the meter or regulator to the appliance. Add 50 percent of that figure to account for fittings. A 60-foot measured run becomes 90 feet of developed length.
Step 3: Read the table. Cross-reference CFH required against developed length in the NFPA 54 Schedule 40 pipe capacity table. Select the smallest pipe size with capacity equal to or greater than the required CFH.
Natural Gas Pipe Sizing Chart
Schedule 40 black iron pipe capacities in BTU/hr at standard residential pressure (0.5-inch water column drop, 7-inch WC inlet, natural gas at 0.60 specific gravity). Based on NFPA 54 Table 402.4(2).
| Pipe Size | 10 ft | 20 ft | 30 ft | 50 ft | 75 ft | 100 ft |
|---|---|---|---|---|---|---|
| 1/2" | 175,000 | 119,000 | 94,000 | 71,000 | 57,000 | 49,000 |
| 3/4" | 360,000 | 246,000 | 196,000 | 147,000 | 119,000 | 103,000 |
| 1" | 680,000 | 464,000 | 370,000 | 279,000 | 224,000 | 194,000 |
| 1-1/4" | 1,400,000 | 960,000 | 764,000 | 578,000 | 465,000 | 403,000 |
3/4-inch pipe handles most single-appliance outdoor runs under 75 feet. A 1-inch line is required when the run exceeds 100 feet or when a fire table and patio heater share the same supply branch.
Fire Pit and Outdoor Appliance BTU Reference
| Appliance | Typical BTU Range | CFH Required | Min Pipe at 50 ft Run |
|---|---|---|---|
| Gas fire pit (standard) | 40,000–65,000 | 40–65 CFH | 1/2" (marginal at 65K) |
| Fire table (high-output) | 65,000–90,000 | 65–90 CFH | 3/4" |
| Large fire pit | 80,000–150,000 | 80–150 CFH | 3/4" to 1" |
| Gas patio heater | 30,000–65,000 | 30–65 CFH | 1/2" |
| Gas fireplace | 30,000–80,000 | 30–80 CFH | 1/2" to 3/4" |
| Fire pit + patio heater (combined) | 80,000–130,000 | 80–130 CFH | 3/4" to 1" |
A 1/2-inch line at 50 feet tops out at 71,000 BTU, marginal for high-BTU fire pits and undersized for any fire table. Most outdoor fire appliance installations benefit from starting with 3/4-inch pipe. Gas fire pits list BTU output on every product page. Large fire pits include commercial-grade burner options above 100K BTU.
How to Measure Developed Length for an Outdoor Run
Developed length is where most outdoor installation errors happen. Installers measure the straight-line distance from the meter to the fire pit location and use that figure directly. That understates the actual run length.
Developed length includes every foot of pipe plus the equivalent length of each fitting. A 40-foot underground run with 3 elbows and a manifold tee can easily reach 65 to 70 feet of developed length. Add 50 percent to the measured pipe footage as a quick field estimate; use fitting-by-fitting calculation when the run approaches the pipe's capacity limit.
When 2 PSI Service Changes the Calculation
Standard residential service runs at 7-inch water column, roughly 0.25 PSI. The ICC's fuel gas pipe sizing guidance notes that 2 PSI service is common when loads exceed what standard pressure can deliver over long runs.
For higher-demand installations, a separate natural gas pipe sizing chart 2 psi table (NFPA 54 Table 402.4(8)) governs sizing at medium pressure, with capacities roughly 4 to 6 times higher at the same pipe size and run length.
Worked Examples
Example 1: Single Fire Pit, 50-Foot Run, Standard Pressure
Appliance: 60,000 BTU natural gas fire pit. Run: 40 feet measured + 50% = 60 feet developed length.
CFH required: 60,000 / 1,000 = 60 CFH. From table at 75 ft: 3/4" pipe = 119,000 BTU capacity (119 CFH).
Result: 3/4-inch pipe handles this load at 60 feet with 59,000 BTU of spare capacity for future additions.
Example 2: Fire Table + Patio Heater, 80-Foot Run, Shared Line
Appliances: 75,000 BTU fire table + 50,000 BTU patio heater = 125,000 BTU combined. Run: 60 feet measured + 50% = 90 feet developed length.
CFH required: 125,000 / 1,000 = 125 CFH. From table at 100 ft: 3/4" = 103,000 BTU (103 CFH), insufficient. 1" pipe at 100 ft = 194,000 BTU (194 CFH), adequate.
Result: 1-inch pipe required. Running 3/4-inch to the first appliance then splitting to 1/2-inch branches is not acceptable. The 3/4-inch trunk must cover the combined load at full run length first.
Example 3: Adding a Fire Pit to an Existing 3/4-Inch Line
Existing system: furnace (80,000 BTU) + water heater (40,000 BTU) = 120,000 BTU existing load. Existing 3/4-inch main run: 50 feet developed length (from table: 147,000 BTU capacity). New fire pit: 60,000 BTU at 70 feet developed length to the pit location.
New total load: 120,000 + 60,000 = 180,000 BTU. 3/4-inch at 70 feet: approximately 125,000 BTU (between 50-ft and 75-ft table values).
Result: Existing line fails. A dedicated 1-inch run from the meter to the fire pit is required. Tapping the existing 3/4-inch line will starve both the existing appliances and the fire pit under simultaneous load.
What to Do When an Existing Line Is Too Small
Adding a fire pit or outdoor fireplace to an existing gas system is the most common gas line sizing scenario homeowners face. Three options, in order of practicality.
Run a dedicated line from the meter. This is the cleanest solution. A dedicated 3/4-inch or 1-inch run from the meter or the main supply manifold eliminates the interaction with indoor appliances. The gas line size calculator should be run for this run independently, using only the outdoor appliance BTU load.
Install a 2 PSI service. For very long runs or loads above 200,000 BTU, coordinating with the utility to deliver 2 PSI to a dedicated outdoor regulator is an option. A licensed gas fitter must make the connection.
What Your Result Means
Browse propane fire pits at Fire Pit Surplus with BTU ratings on every product page. For indoor gas options, fireplaces include BTU output in product specs for direct input into this calculator.
Frequently Asked Questions
What size gas line do I need for a fire pit?
Most backyard fire pits run 40,000 to 65,000 BTU. At a 50-foot run, a 3/4-inch Schedule 40 pipe handles up to 147,000 BTU at standard pressure drop. A 1/2-inch line at that length tops out near 71,000 BTU, which is marginal for high-BTU fire tables or dual-burner units.
How do I calculate gas pipe size for natural gas?
Divide the appliance BTU rating by 1,000 to get cubic feet per hour required. Then find which pipe diameter handles that CFH at your run length using the NFPA 54 table above. Add 50 percent to actual pipe length to account for elbows and tees before reading the table.
What is the gas pipe sizing table based on?
This chart follows NFPA 54 Table 402.4(2), sizing Schedule 40 black iron capacity in BTU per hour by pipe diameter and run length at 0.5-inch water column drop. These values apply to standard residential service at 7-inch WC inlet with natural gas at 0.60 specific gravity.
Does a longer gas line need a bigger pipe?
Yes. Pressure drop accumulates over distance, reducing flow at the appliance. A 3/4-inch pipe handles 147,000 BTU at 50 feet but only 103,000 BTU at 100 feet. Longer outdoor runs to fire pits and patio heaters often require stepping up one pipe size to maintain full output.
Can I add a fire pit to an existing gas line?
Only if the existing line has capacity to spare after all appliances run simultaneously. Add the fire pit BTU to the total load and run the gas line size calculator for the full length from the meter. If the result exceeds the pipe's rated capacity, a dedicated new run is needed.
What is a 2 PSI gas line and when do I need it?
Standard residential service runs at 7-inch water column, about 0.25 PSI. A 2 PSI medium-pressure line carries roughly 8 times more capacity at the same pipe size. High-BTU outdoor appliances and runs over 100 feet benefit from 2 PSI service with a regulator at the appliance.
Final Thoughts
Gas line sizing comes down to two numbers: the CFH demand at full load, and the developed length from meter to appliance. This gas pipe size calculator returns the minimum diameter that satisfies both. An undersized line does not fail dramatically — it just underperforms every session, and the fire pit never burns at what the spec sheet promised.
Confirm pipe size and system pressure with a licensed gas fitter before finalizing the run design.
Gas line size calculations are based on NFPA 54 Table 402.4(2) for Schedule 40 black iron pipe at standard residential pressure. Actual capacity varies by pipe material, fittings, and local gas specific gravity. Always verify final sizing with a licensed professional.
