Gas rate / heat input

Work out gross and net heat input from your own meter readings — metric timed volume or the imperial test-dial method. Everything is worked out on your device.

Works with these meters (natural gas):

Metric — any meter reading in m³: G4 and G10-class diaphragm (incl. dual-badged U16/G10), E6 and other smart/electronic meters.

Imperial — meters with a test dial marked 1 or 2 ft³ per revolution (typically U6 domestic meters; the dial size is printed on the dial face).

Not for LPG metering. If your meter doesn't read m³ or carry a 1–2 ft³ test dial, this calculator's constants don't apply.

Measurement method

Metric (digital)Imperial (test dial)

Start reading (m³)

End reading (m³)

Time (seconds)

Default 120 s, or time it: Start at the first reading, Stop at the second. Editable.

Gross heat input— kW

Net heat input— kW

Gross heat input— BTU/h

Flow rate— m³/h

Tolerance check against a declared figure (optional)

Manufacturer's declared input (kW)

That figure is

Net (usual)Gross

Data-plate figures are usually net.

Constants: metric ×10.76, gross → net ÷1.11, kW ↔ BTU/h ×3412, to the nearest 10. Method: industry-standard gas-rate method (LCL Awards Domestic manual, Issue 5.3).

Working with a smart / electronic meter

Electronic and smart meters have no test dial, so use the Metric (digital) method above — not imperial.

They sleep to save battery, so wake the display before you read it: press the meter's button, or let it wake by itself once gas flows when you run the appliance.

Take a start reading. Read the consumption figure in m³ — usually to three decimals.
Run the appliance at full rate and time your window.
Take the end reading the moment the time is up.

The difference between the two is your volume. Enter both readings and the time above, and the calculator does the rest.

Meters vary by make and model. If you're not sure how a particular meter works, check that meter's own guidance.

A calculation aid, not an assessment. It computes heat input from the readings you enter. It does not assess, approve or determine whether an appliance is safe or correctly set — that is the engineer's determination, from the appliance's own tests and the manufacturer's instructions.

Natural gas only in this version; LPG is a fast-follow. Method: the industry-standard gas-rate method as set out in the LCL Awards Domestic Gas Safety training manual, Issue 5.3.

Something look wrong in this calculator? Tell us — it is the most useful message you can send.