Hi,
When gas is delivered to your home, it's measured by your meter in cubic metres. Your energy supplier will then convert this figure to kWh to simplify the billing process. A kWh is an amount of energy equal to 1 kilowatt (1000 Watts) operating for one hour.
To calculate, simply multiply your meter reading by a "correction factor" of 1.022640 http://www.uswitch.com/gas-electricity/energy-bill-glossary/. And then multiply by the "calorific value" - this should be shown on your gas statement. The figure is usually around the 40 mark. National Grid provides suppliers with a daily value and we work out an average for the period covered by your statement.
Finally, the figure is divided by 3.6 (the "kWh conversion factor").
For more info, please look at http://www.energylinx.co.uk/gas_meter_conversion.html. You'll also find a brief explanation on the back of your energy statement.
