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Gas Pipe Size Calculator
For natural gas systems
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How to use this gas pipe size calculator
Step 1: Enter a gas rate. Gross and net values will be automatically calculated for your reference.
Step 2: Enter the pipe length and all the fittings you plan on using for this section.*
Step 3: Some initial results will now appear on the right side. If the pressure drop displays red, the pipe diameter is too small. Adjust the pipe type until a green result appears. A green result indicates an acceptable pressure drop of less than 1 mbar for natural gas.
* For gas systems with multiple sections, you will need to do a separate calculation for each and then add up the total pressure loss.
If the property’s gas system contains more than one appliance or section, you must first break down the system into each section with separate lengths and gas rate numbers. At the end, total up the pressure drop and ensure it is below the accepted 1 mbar max.
Why use a gas pipe size calculator?
Save time
Our gas pipe size calculator will help you find the right size pipe far quicker than any manual calculation.
Get more done
The faster you know what you need to be doing, the quicker you get it done and move onto the next job.
Make fewer mistakes
Calculations done by hand are prone to human error. Get it right every time with a reliable
formula.
How to manually calculate pipe sizes for gas systems
The first thing you’ll need is access to some gas pipe size datasheets. Up-to-date tables for copper and steel pipes using natural gas and LPG can be found in the BS 6891:2015 document.
Step 1: Calculate the maximum gas rate of the appliance. To do this, you can multiply the maximum heat input (kW) by 0.095.
Step 2: Add up the total pipe length. This will include straight length of the pipe (m) and any fittings, which have the following equivalent lengths:
| Steel | Copper | 45° | 90° | 90° elbow | Tee entering | Tee exiting |
| ≤1/2 inch | ≤15mm | 0.15 | 0.20 | 0.40 | 0.75 | 1.20 |
| 3/4 inch | 22mm | 0.20 | 0.30 | 0.60 | 1.20 | 1.80 |
| 1 inch | 28mm | 0.25 | 0.40 | 0.80 | 1.50 | 2.30 |
| 1 1/4 inch | 35mm | 0.30 | 0.50 | 1.00 | 2.00 | 3.00 |
Step 3: Add up a total equivalent pipe length
Step 4: Cross-reference table A.1 or A.2 in BS 6891:2015 and guesstimate for an appropriate pipe size and it’s corresponding pressure loss per meter figure.
Step 5: Multiply the pressure loss per meter number by your total equivalent length (m) for a total pressure loss.
Step 6: If the total pressure loss is greater than 1mbar, repeat the process with a larger pipe diameter,
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