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Gas Meter Timer Calculator — Test Dial Timing
Time the test dial on a gas meter to calculate gas rate and compare against the appliance rated input. Default ±5% tolerance is editable.
Time for one full revolution of the test dial
Volume per revolution (usually 0.01 m³)
UK default 39.5 MJ/m³
Standard 1.02264
Acceptable deviation. ACS practice typically uses ±5%; Worcester Bosch quote +5%/−10% for natural gas. Always check the appliance’s own commissioning instructions.
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How We Calculate This
This calculator uses the test dial timing method to determine gas rate. Gas Safe engineers routinely use this during commissioning and annual servicing to verify appliance performance.
Formula
- Gas rate (m³/hr): (dial size ÷ seconds per rev) × 3600 × correction factor
- kW gross: (m³/hr × CV × 1000) ÷ 3600
- Deviation: ((measured kW − rated kW) ÷ rated kW) × 100
- Expected seconds: Reverse-calculated from rated input for comparison
There is no single Gas Safe Register tolerance figure. ACS practice typically works to roughly ±5%, while Worcester Bosch quote +5%/−10% for natural gas, so the tolerance here is editable (default ±5%). Always follow the appliance’s own commissioning instructions. If the deviation exceeds the expected band, the engineer should investigate gas pressure, burner condition, and meter accuracy before signing off the appliance.
Note: presets are gross rated input. Confirm whether your data badge Qn is quoted gross or net before reading the deviation — most UK badges quote gross, but some quote net.
Frequently Asked Questions
Isolate all other gas appliances. Fire the target appliance at full rate. Using a stopwatch, time how many seconds it takes for the smallest dial (test dial) on the meter to complete one full revolution. The test dial typically represents 0.01 m³. Record the time in seconds.
There is no single Gas Safe Register figure. As a working rule, ACS practice typically expects the measured input within roughly ±5% of the rated figure on the data badge, while Worcester Bosch quote an asymmetric +5%/−10% for natural gas. The tolerance in this calculator is editable for that reason. Always check the appliance’s own commissioning instructions. If the measured rate falls outside the expected band, investigate the gas valve setting, burner pressure, or supply pressure.
Most UK metric gas meters have a test dial that represents 0.01 m³ (10 litres) per revolution. Some older or larger meters may have 0.1 m³ dials. Check the meter face markings to confirm the dial value.
Minor differences are normal due to gas pressure variations, calorific value changes, and meter accuracy. Also confirm whether the badge quotes gross or net heat input, as comparing the wrong one shifts the result by about 10%. If the deviation is larger than expected, check the burner pressure at the test point, the gas supply pressure (21 mbar for natural gas), and that no other appliances are using gas. Use our Gas Rate Calculator to convert meter readings into kW for a full comparison with the data badge.
Most UK appliance badges (and the Gas Safe Register) quote gross heat input, but some manufacturers quote net, so always check which the badge shows. For natural gas, divide gross by 1.11 to get net (net is about 90% of gross), or multiply net by 1.11 to get gross. This calculator headlines the measured gross figure and also shows the net value in the breakdown, so you can compare against whichever your badge quotes.
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Last updated: June 2026
Verified against UK standards · estimates only, confirm with your supplier.