Converts a timed meter dial test to heat input (kW) and compares it against an appliance's data-badge rating.
Commissioning check per Gas Safe Register Technical Bulletin 141. Verify with your own manufacturer tolerance where available.
For commissioning guidance only. Always verify with a qualified Gas Safe registered engineer.
About this gas rate calculator
This free gas rate calculator turns a timed gas meter dial test into an appliance heat input in kilowatts and compares it against the data-badge rating, as a commissioning and fault-finding check. It handles both metric (m³) and imperial (ft³) meters, natural gas and LPG, and net or gross rated bases, and returns a pass / over-gassed / under-gassed verdict to the tolerance in Gas Safe Register Technical Bulletin 141. It is aimed at UK Gas Safe registered engineers and heating contractors checking appliances on site. Everything runs in your browser. Nothing is uploaded.
How the gas rate is calculated
The volumetric rate is (test volume ÷ test time) × 3600 to give m³/h; an imperial dial test is read as ft³ per revolution and converted at 0.0283168 m³/ft³. Heat input is then rate × calorific value ÷ 3.6 (since 1 kWh = 3.6 MJ). Calorific values follow the BPEC LPG Changeover (CoNGLP1) figures: natural gas 34.9 (net) / 38.76 (gross) MJ/m³, LPG 86.1 (net) / 93.1 (gross) MJ/m³, and the measured input is compared on whichever basis the appliance badge uses (net is the UK norm). The deviation from the rated input is checked against the default +5% / −10% band from TB141, both editable.
Frequently asked questions
Should I use the net or gross rating?
Use the basis printed on the appliance data badge. UK appliance ratings are normally quoted net, so the default is net; switch to gross only if the badge states a gross figure. The tool works out both the net and gross heat input, then compares the one matching your selected basis against the rating.
What is the standard meter test?
For a metric meter, take a timed reading over a fixed period, a two-minute (120 s) test is common. And enter the volume passed and the time. For an imperial meter, enter the test dial’s volume per revolution (printed at the 12 o’clock position) and the seconds for one revolution. Isolate other appliances so only the one under test is drawing gas.
What do the high and low verdicts mean?
“High” means over-gassed: the measured input exceeds the upper tolerance, which can indicate a corroded or enlarged injector. “Low” means under-gassed, often a partially blocked injector or a supply pressure problem. Both flag the appliance for investigation against the manufacturer’s data and Gas Safe TB141.