Gas pipe sizing charts should not be used to size a pipe in isolation. Doing so is like using a road map without knowing where you’re starting or where you’re going. The chart itself is only a reference tool. Without understanding the full gas system, including total load, distance, and layout, the numbers in the chart are taken completely out of context.
Each pipe segment is sized individually, but always in relation to the entire system it serves. When that context is missing, even a “correct” pipe size on paper can fail in real-world operation.
This guide explains how gas pipe sizing charts work, what information they require, and how to read them correctly without oversimplifying the process. It assumes the gas system has already been mapped and evaluated using an accepted sizing method, most commonly the Longest Run Method.
If you are still in the planning phase and want to understand how a gas system is sized for a fire pit, including meter capacity, trunk and branch layout, and why adding a fire pit can change the entire system, start with our guide to gas pipe sizing for fire pits before using any chart.
What Information Is Required to Use Gas Pipe Sizing Charts?
Pipe sizing charts do not size individual pipes; they size systems. They are essentially “cheat sheets”. They translate the physics of gas flow, friction, and pressure loss into usable numbers for real-world installations.
Rather than measuring each pipe section independently, the charts assume the system has already been mapped and that two critical values are known:
- The Master Length: The total length of the longest run of pipe from the gas meter to the most remote appliance. This length includes vertical runs and any added equivalent length created by fittings and valves.
- Total BTU Demand: The combined BTU load of all downstream appliances being sized.
When these two values are cross-referenced on the correct chart, the result is the minimum pipe diameter required to deliver sufficient gas volume while maintaining stable pressure at every appliance.
This is also why charts are so often misused. If the master length is underestimated, fittings are ignored, or the total BTU load is incomplete, the chart will still return an answer, but it will be wrong. The chart only works when the system data feeding it is accurate.
The sizing method itself, including the Longest Run Method and the calculation of total BTU demand, is covered in more detail in the companion guide linked in the introduction.
The Importance of Using the Correct Chart
Gas pipe sizing charts are not universal. A qualified technician must confirm that the chart matches the specific conditions of the installation, including:
- Gas Type: Natural gas or propane.
- Pipe Material: PE (polyethylene), black iron, copper, etc.
- Pressure Drop: A 0.5-inch WC (Water Column) pressure drop chart is the standard for most residential fire pit installations.
- Specific Gravity: Typically 0.60 for natural gas.
- Meter Pressure: Most homes use low-pressure service (under 2.0 PSI), while newer or high-load systems may use 2.0 PSI.
Warning: Using a chart that does not match the gas type, pipe material, or meter pressure will result in incorrect pipe sizing. Meter pressure must always be verified, and the chart selected must match the actual system conditions.
Local Code Rules
Gas sizing charts and calculation methods are governed by adopted fuel gas codes, which are updated over time. Local jurisdiction is always the final authority for approved projects and inspections.
While the Longest Run Method is widely accepted for its conservative approach and being easily verified, some jurisdictions may also permit the Branch Method. This guide focuses on the Longest Run Method only, as acceptance of alternative methods varies by location.
How Gas Pipe Sizing Charts Are Used
Charts are frequently calculated in Cubic Feet per Hour (CFH) or MBH (Thousands of BTUs per Hour). For practical sizing purposes, they can be treated the same. For conversion purposes, 1,000 BTUs is approximately equal to 1 CFH or 1 MBH.
Once the correct chart is identified, the sizing process follows a strict logical sequence.
Step 1: Lock the Master Length
The row showing the “master length” (the longest run) is selected. If the actual measurement falls between two values, the next longer length is chosen (always size up). This row becomes the only relevant row for sizing every section of the piping system, regardless of the actual length of any specific branch or segment.
Step 2: Cross-Reference BTU Demand
After locking the row, moving horizontally to the right, you find the BTU load applicable to the specific section being sized. If the exact figure is not listed, the next largest figure in that same row is selected.
Result: Pipe Size
The header of the column where the two previous criteria intersect indicates the required pipe diameter for that section of pipe.
Example of using a Pipe Sizing Chart
In a scenario below, a Natural Gas fire pit is the only gas outlet on the longest run from a low-pressure residential gas meter. The underground yard pipe is Polyethylene Plastic with a master length of 110 feet, and the fire pit is rated 75,000 BTUs (75 CFH). The process is as follows:
- Length: The master length (110 feet) is selected from the left-hand column; if the value falls between two figures, the next highest value is chosen (e.g., the 125-foot row).
- Load: Moving across that 125-foot row, the total load equal to or higher than 75 CFH is located. In this case, it would be 103 CFH.
- Result: For natural gas, using PE pipes, at standard low pressure(<2.0PSI), with a pressure drop of 0.5″ (WC), a 3/4-inch pipe is required.
Visual Guide
For those who want to see the math and charts in action, we recommend this technical walkthrough by David Butler at Serving Up Plumbing:
Pipe Sizing Chart Examples
The charts here are provided for general information and understanding only. They’re a helpful reference, not a replacement for a professionally designed system.
About the natural gas charts
The two natural gas (NG) charts below are for metallic pipe and PE plastic pipe, the most common materials used in residential outdoor NG installations. Both apply to low-pressure natural gas only, delivered at less than 2 psi, which is the standard service pressure in most homes.
About the propane charts
The two propane charts below are also for metallic pipe and PE plastic pipe. Both apply after the gas has been regulated down to low pressure: 11 inches water column (0.4 psi), which is the standard pressure at the appliance in a whole-house propane system. If your fire pit is a long way from the tank, your gas technician may run a higher-pressure line to a point closer to the pit and step it down locally. The charts apply to the pipe after the step down.
Charts:
- Natural Gas: Schedule 40 Black Iron Pipe
- Natural Gas: PE Plastic Pipe
- Liquid Propane: Metallic Pipe
- Liquid Propane: PE Plastic Pipe
The Role of the Licensed Professional
While charts provide the data, gas line installation is restricted to licensed professionals. Certified technicians ensure the work meets safety standards, adheres to permit requirements, and protects homeowner insurance eligibility.
Adherence to NFPA 54 and local codes protects both the property and its occupants. Engaging an expert early prevents costly infrastructure mistakes and ensures the fire pit operates at its intended capacity.
Risks of Improper Sizing and Installation:
- Performance Failure: Appliances may fail to meet flow and pressure requirements, leading to “lazy” flames or ignition issues.
- System Noise: Undersized pipes can cause excessive whistling or humming.
- Mechanical Strain: Incorrect pressure can strain valves and fittings, reducing the lifespan of appliances.
- Safety Hazards: Improperly installed lines can trigger leaks or blockages, creating significant fire and health risks.
Conclusion: Putting Gas Pipe Sizing Charts in Context
Gas pipe sizing charts are powerful tools, but only when they are used in the right context. They are not shortcuts, and they are not meant to be applied to a single pipe run without understanding the system it belongs to.
When the master length, total BTU demand, gas type, pressure, and pipe material are all correctly identified, a sizing chart provides a reliable answer. When any of those inputs are wrong or incomplete, the chart still produces a number, but that number no longer reflects reality.
This is why professionals treat charts as the final step, not the starting point. The real work happens before the chart is ever opened, mapping the system, confirming capacity, and selecting the correct method and code requirements for the jurisdiction.
Used correctly, sizing charts help ensure stable pressure, proper flame performance, and long-term system reliability. Used in isolation, they are one of the most common causes of undersized gas lines and underperforming fire pits.