Gas Meter Flow Rate Calculator
Determine the Cubic Feet per Hour (CFH) and BTU output by clocking the gas meter.
0.5 cu ft
1 cu ft
2 cu ft
5 cu ft
10 cu ft
Select the size marked on the meter's proving dial.
Time taken for the dial to make one full rotation.
Standard natural gas is approx 1,000 – 1,050 BTU/ft³.
Leave as 1.0 for standard low-pressure residential meters.
Calculation Results
Volumetric Flow Rate:
– CFH
Energy Input Rate:
– BTU/hr
Energy Output (at 80% Efficiency):
– BTU/hr
Energy Output (at 95% Efficiency):
– BTU/hr
How to Calculate Natural Gas Flow Rate
Calculating the natural gas flow rate is an essential skill for HVAC technicians and engineers to verify that gas appliances (furnaces, boilers, water heaters) are firing at their rated input capacity. The most common method used in the field is "clocking the meter."
The Gas Flow Formula
To determine the volumetric flow rate in Cubic Feet per Hour (CFH), we use the relationship between the volume of the test dial and the time it takes to complete a revolution. The formula is:
CFH = (3600 × Dial Size × Pressure Factor) / Seconds
- 3600: The number of seconds in one hour.
- Dial Size: The volume of gas measured in one full revolution of the test dial (usually 0.5, 1, 2, or 5 cubic feet).
- Seconds: The stopwatch time for one full revolution.
- Pressure Factor: Usually 1.0 for standard residential pressures (7″ w.c.). High-pressure systems require compensation.
Converting CFH to BTU/hr
Once you have the flow rate in cubic feet, you can convert this to British Thermal Units (BTU) per hour to compare against the appliance's rating plate. You multiply the CFH by the caloric value of the gas.
BTU/hr = CFH × Heating Value (BTU/ft³)
While the exact heating value of natural gas varies by region and supplier, the following averages are commonly used:
- Standard Natural Gas: ~1,000 to 1,050 BTU/ft³
- Propane (LP): ~2,500 BTU/ft³
Step-by-Step: How to Clock a Gas Meter
- Turn off all other gas appliances in the building to ensure only the unit being tested is drawing gas.
- Turn the appliance to be tested to its maximum firing rate (high fire).
- Locate the test dial on the gas meter. It is usually the smallest dial marked "1/2 ft", "1 ft", or "2 ft".
- Using a stopwatch, time exactly how many seconds it takes for the dial to make one complete revolution.
- Enter the dial size, seconds, and local gas heating value into the calculator above to determine the input rate.
If the calculated BTU/hr is significantly lower or higher than the manufacturer's rating plate (typically within +/- 5%), adjustments to the manifold pressure or orifice size may be necessary.