How do I time the test dial on a gas meter?

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.

What is the ±6% tolerance for gas rate?

Industry guidance from Gas Safe Register states that the measured gas rate should be within ±6% of the appliance's rated input shown on the data badge. If outside this tolerance, the gas valve setting, burner pressure, or supply pressure may need investigation.

What size is the test dial on a UK gas meter?

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.

Why does my gas rate differ from the data badge?

Minor differences are normal due to gas pressure variations, calorific value changes, and meter accuracy. If outside ±6%, 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.

How do I convert between kW gross and kW net for the data badge?

Some manufacturers quote gross input, others net. For natural gas, kW net is approximately 90% of kW gross. If the data badge shows net input, multiply by 1.11 to get gross, or divide gross by 1.11 to get net. Always check which value the manufacturer has quoted.

TradeCalculator

Gas Meter Timer Calculator — Test Dial Timing

Time the test dial on a gas meter to calculate gas rate and compare against appliance rated input within the industry-standard ±6% tolerance.

Seconds Per Revolution

Time for one full revolution of the test dial

Test Dial Size

Volume per revolution (usually 0.01 m³)

Appliance Type

Select appliance or enter custom rated input

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

The ±6% tolerance is an industry-accepted margin. If the deviation exceeds this, the engineer should investigate gas pressure, burner condition, and meter accuracy before signing off the appliance.

Frequently Asked Questions

Related Calculators

Pipe Sizing Calculator

Calculate the correct pipe diameter for your plumbing installation.

Boiler Size Calculator

Determine the right boiler kW output for your UK property.

Hot Water Cylinder Sizing Calculator

Size your hot water cylinder based on household demand.

Radiator Sizing Calculator

Calculate the BTU output needed for each room.

Central Heating System Volume Calculator

Calculate total water volume in your central heating system.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.