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Gas Pipe Sizing Calculator

Work out gas pipe sizing instantly with clear inputs, formula shown and shareable results.

About Gas Pipe Sizing Calculator

Low-pressure fuel gas piping is sized by the longest-length method. Connected load divided by heating value gives the cubic feet per hour to deliver, and the low-pressure flow equation Q = 2313 D^2.623 (Δp / (Cr L))^0.541 is inverted to find the bore, with Cr = 0.6094 for natural gas at 0.60 specific gravity.

Formulas

Gas flow capacity

Q = 2313 x D^2.623 x (Δp / (Cr x L))^0.541

Q
ft³/h
D
Inside diameter, in
Δp
Pressure drop, in.wg
L
Length, ft
Cr
0.6094 for 0.60 SG natural gas

Required flow

ft³/h = connected load BTU/h / heating value BTU/ft³

Worked example

With the default values below, Gas Pipe Sizing Calculator returns Bore required of 1.047. Change any input above and every figure here is recalculated in your browser.

Inputs used

Connected gas loadminimum 1 BTU/h
200,000 BTU/h
Gas heating valueminimum 100 BTU/ft³
1,030 BTU/ft³
Longest run lengthminimum 1 ft
100 ft
Allowable pressure dropminimum 0.05 in.wg
0.5 in.wg

Results

Bore required
1.047 in
Nominal pipe size to use
1-1/4 in
Gas flow required
194.2 ft³/h
Capacity of chosen size
309 ft³/h

Step by step

  1. 1Values used
  2. 2Gas flow capacity
  3. 3Required flow
  4. 4Bore required= 1.047 in
  5. 5Nominal pipe size to use= 1-1/4 in
  6. 6Gas flow required= 194.2 ft³/h
  7. 7Capacity of chosen size= 309 ft³/h

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Fuel gas piping must be sized and installed by a licensed professional to the applicable fuel gas code.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Fuel gas piping must be sized and installed by a licensed professional to the applicable fuel gas code.

Frequently Asked Questions

How is the Gas Pipe Sizing figure worked out?

Q = 2313 x D^2.623 x (Δp / (Cr x L))^0.541. Low-pressure fuel gas piping is sized by the longest-length method.

Do fittings need to be added to the length?

The longest-length method already carries an allowance for normal fittings. Unusual arrangements with many elbows or a long flexible connector should be checked by the equivalent length method instead.

What values do I need to enter?

This calculator takes 4 inputs: Connected gas load, Gas heating value, Longest run length, Allowable pressure drop. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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