How do I calculate gas rate from meter readings?

Turn off all other gas appliances and take a meter reading. Turn on only the appliance you want to test at full rate. After a timed period (typically 90 seconds minimum), take a second reading. The difference is the gas consumed. This calculator converts that volume and time into m³/hr, kW and BTU/h.

What is the gas correction factor 1.02264?

The correction factor of 1.02264 adjusts the metered volume of gas to standard conditions of temperature (15°C) and pressure (1013.25 mbar). This is the standard factor used by UK gas suppliers and Gas Safe engineers for billing and commissioning calculations.

What is the difference between kW gross and kW net?

kW gross (also called higher heating value) includes the latent heat in water vapour produced during combustion. kW net (lower heating value) excludes this. UK boiler ratings typically use kW net for output but kW gross for gas input. The ratio is approximately 0.9 for natural gas.

What calorific value should I use?

UK natural gas has a calorific value of approximately 39.5 MJ/m³. Your gas supplier publishes the exact CV on their website — it typically ranges from 37.5 to 43.0 MJ/m³. Using the correct CV gives a more accurate kW calculation.

Why is gas rate important for boiler commissioning?

Gas Safe engineers must check the gas rate during boiler commissioning to verify the appliance is burning gas at the correct rate stated on the data badge. An incorrect gas rate could indicate a fault with the gas valve, burner or gas supply pressure.

Gas Rate Calculator &mdash; Convert kW, BTU/h & m&sup3;/hr

Gas Rate Calculator — Convert kW, BTU/h & m³/hr

Calculate gas consumption rate from meter readings. Convert between kW, BTU/h and m³/hr for boiler commissioning and gas safety checks.

Meter Reading Start

Initial gas meter reading before test

Meter Reading End

Final gas meter reading after test

Time Elapsed

Duration of test (minimum 90 seconds recommended)

Meter TypeMetric meters read in m³, imperial in ft³

How We Calculate This

The gas rate calculator converts meter readings into useful engineering units for boiler commissioning and gas appliance testing. This is a core skill for Gas Safe registered engineers.

Calculation method

Volume used: End reading minus start reading
Imperial conversion: ft³ × 0.0283168 = m³
Corrected volume: m³ × 1.02264 (temperature & pressure correction)
Gas rate: (corrected m³ ÷ seconds) × 3600 = m³/hr
kW gross: (m³/hr × CV × 1000) ÷ 3600
kW net: kW gross × 0.9
BTU/hr: kW gross × 3412.14

Always ensure all other gas appliances are turned off when testing a single appliance. The test should run for a minimum of 90 seconds for accuracy. Refer to the appliance data badge to compare the calculated gas rate against the manufacturer's stated input.