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Gas Flow Rate Calculator

Work out gas flow rate instantly with clear inputs, formula shown and shareable results.

About Gas Flow Rate Calculator

Gas flow is simply input rating divided by heating value. The clocking time is the practical field check: with all other appliances off, timing one cubic foot on the meter dial should match 3600 divided by the calculated flow, which confirms the appliance is firing at its nameplate rate.

Formulas

Gas flow

ft³/h = input BTU/h / heating value BTU/ft³

Meter clocking

seconds per ft³ = 3600 / (ft³/h)

Worked example

With the default values below, Gas Flow Rate Calculator returns Gas flow rate of 145.63. Change any input above and every figure here is recalculated in your browser.

Inputs used

Appliance input ratingminimum 1 BTU/h
150,000 BTU/h
Gas heating valueminimum 100 BTU/ft³
1,030 BTU/ft³

Results

Gas flow rate
145.63 ft³/h
Flow in cubic metres
4.124 m³/h
Clocking time per cubic foot
24.7 s
Energy rate
1.500 therms/h

Step by step

  1. 1Values used
  2. 2Gas flow
  3. 3Meter clocking
  4. 4Gas flow rate= 145.63 ft³/h
  5. 5Flow in cubic metres= 4.124 m³/h
  6. 6Clocking time per cubic foot= 24.7 s
  7. 7Energy rate= 1.500 therms/h

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges 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.

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

Frequently Asked Questions

How is the Gas Flow Rate figure worked out?

ft³/h = input BTU/h / heating value BTU/ft³. Gas flow is simply input rating divided by heating value.

What if the clocked time is much shorter than predicted?

The appliance is overfiring, usually from high manifold pressure or a wrong orifice. Both waste fuel and can produce carbon monoxide.

What values do I need to enter?

This calculator takes 2 inputs: Appliance input rating, Gas heating value. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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