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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.
Initial gas meter reading before test
Final gas meter reading after test
Test duration. Metric meters: 120 s (2 min) is the long-standing convention; Gas Safe TB 162 (2023) also permits 60 s (1 min). Imperial: time one full dial revolution.
Gross calorific value. UK billed CV is held within 38–41 MJ/m³ (gov.uk); 39.5 is the representative default. Use your supplier’s published CV for best accuracy.
Temperature/pressure correction (standard 1.02264)
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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 (rounded UK conversion for natural gas; precise factor is ÷ 1.108 = × 0.9026 per gov.uk DUKES Annex A)
- BTU/hr: kW gross × 3412.14 (1 kW = 3412.14 BTU/h)
Always ensure all other gas appliances are turned off when testing a single appliance. For metric meters, time the test over 2 minutes (120 s) — the long-standing convention — or 1 minute (60 s), now permitted by Gas Safe Technical Bulletin 162 (2023); for imperial meters, time one complete dial revolution. Refer to the appliance data badge to compare the calculated gas rate against the manufacturer's stated input.
Frequently Asked Questions
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 — 2 minutes (120 s) is the long-standing convention for metric meters, though Gas Safe Technical Bulletin 162 (2023) now also permits 1 minute (60 s); for imperial meters, time one complete dial revolution — take a second reading. The difference is the gas consumed. This calculator converts that volume and time into m³/hr, kW and BTU/h. For timing the meter test dial, use our Gas Meter Timer Calculator.
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.
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.
UK natural gas has a gross calorific value of approximately 39.5 MJ/m³, the representative figure used in gov.uk billing examples. Gas transporters are required to hold the billed CV within 38–41 MJ/m³, and your supplier publishes the exact daily CV for your area. Using the correct CV gives a more accurate kW calculation.
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. Use our Gas Pipe Sizing Calculator to check the pipework is adequate for the appliance load.
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Last updated: June 2026
Verified against UK standards · estimates only, confirm with your supplier.