FreeHVACCalculators

Start here

Menu

Gas Meter Clocking Calculator

Find a gas appliance’s actual firing rate by timing the gas meter’s test dial, and see how far it is from the nameplate input.

Method reviewed October 25, 2026. Version 1.0.0. How it works

Your inputs

Unit system

Seconds, from a stopwatch.

Timing two or more revolutions improves accuracy.

BTU per cubic foot. 1,036 is the EIA U.S. average for natural gas; your utility can give the local value. For propane vapour, use your supplier’s figure.

Result

Measured gas input
93,240BTU/h
Gas flow
90ft³/h
Difference from nameplate input
3.6%

About 93,240 BTU/h of gas input (90 ft³/h).

  • Turn off every other gas appliance (including pilots) and let the burner run steadily on high fire before timing. The result is input, not output: output ≈ input × efficiency.
Show the working
  1. Gas flow = 3,600 × dial size ÷ seconds per revolution
    3,600 × 0.5 ÷ 20 = 90 ft³/h
  2. Input = gas flow × heating value
    90 × 1,036 = 93,240 BTU/h
  3. Difference = measured ÷ nameplate − 1
    93,240 ÷ 90,000 − 1 = 3.6 %

How to clock a meter

  • Turn off every other gas appliance on the meter, including standing pilots.
  • Run the appliance on high fire for a few minutes so it is steady.
  • Find the test dial on the meter, the smallest dial, and note its size (½, 1 or 2 cubic feet per revolution are common).
  • Time one or more full revolutions with a stopwatch.

Gas flow in cubic feet per hour is 3,600 × dial size × revolutions ÷ seconds. Multiply by the gas heating value to get BTU/h of input.

Heating value

The default is the EIA’s U.S. average for natural gas, 1,036 BTU per cubic foot. Your utility’s figure is better: it is usually printed on the bill (sometimes as a “therm factor”) and may already be corrected for the pressure and altitude of your area. At high altitude the heating value per cubic foot of gas at the meter is lower.

Reading the result

Manufacturers commonly ask for the measured input to be within a few percent of the nameplate (often ±2 %, check the installation manual). A large difference points to the manifold pressure, the orifices or the gas type, and should be corrected by a qualified technician. The result is input; the heat delivered is input × the furnace’s steady-state efficiency.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

Test dial size
½ cubic foot
Time for the revolutions
20
Revolutions timed
1
Gas heating value
1,036
Nameplate input (optional)
90,000 BTU/h

Result

Measured gas input
93,240 BTU/h
Gas flow
90 ft³/h
Difference from nameplate input
3.6 %

About 93,240 BTU/h of gas input (90 ft³/h).

Assumptions

  • Gas flow from the meter’s test dial: 3,600 seconds per hour × cubic feet per revolution ÷ seconds per revolution. Heating value per cubic foot from your utility (EIA average 1,036 BTU/ft³ for natural gas).

Limitations

  • Meter readings are at the meter’s pressure and temperature; utilities correct the heating value for this, so use their figure where accuracy matters.
  • Only a qualified technician should adjust gas pressure or orifices.

Frequently asked questions

What if my meter has no test dial?

Many newer digital and smart meters show flow differently. Some show a test mode or flow rate on the display; your utility can tell you how to read it.

How long should I time the dial?

At least one full revolution, and longer for small appliances. Timing several revolutions reduces the error from starting and stopping the stopwatch.

Can I clock a propane appliance?

Not with a utility meter, because propane systems rarely have one. Propane input is checked with manifold pressure and orifice size from the manufacturer’s data.

Sources

  1. How to Clock a Gas Meter — A. Pacilla, Plumber magazine (2021). Turn off other gas appliances, time the test dial; a ½ ft³ dial at 20 s per revolution is 90 ft³/h, about 90,000 BTU/h at 1,000 BTU/ft³.
  2. Energy explained — British thermal units (Btu) — U.S. Energy Information Administration. 100,000 Btu per therm; 1,036 Btu/ft³ natural gas; 91,452 Btu/gal propane; 138,500 Btu/gal heating oil; 3,412 Btu/kWh.

Spotted an error? Report a problem with this calculator — see our corrections policy.