Gas Rate Calculator UK

A gas rate calculator is a tool used by Gas Safe registered engineers to calculate the heat input (in kilowatts) of gas appliances. It uses meter readings or test dial measurements to determine if an appliance is operating within its rated capacity.

Gross kW is the total heat input including the latent heat in water vapour. Net kW (gross ÷ 1.11) is the usable heat output. Most appliance data plates show net kW, so compare your calculated net kW to the appliance rating.

Use metric mode if your gas meter displays readings in cubic metres (m³). Use imperial mode if you're using a test dial gauge that measures in cubic feet (cu ft). Most modern UK meters are metric.

For metric mode, run the test for at least 2 minutes (120 seconds) to get an accurate reading. For imperial mode with a test dial, time one complete revolution of the dial - faster-burning appliances will complete a revolution quicker.

This calculator uses 39.5 MJ/m³, which is the typical calorific value for UK natural gas. The actual CV can vary slightly (typically 37.5-43.0 MJ/m³), but 39.5 is the standard used for most calculations.

Small variations (±5%) are normal due to gas pressure, calorific value variations, and measurement timing. Larger differences may indicate a fault, incorrect burner pressure, or a need for servicing. Always follow Gas Safe procedures.