Formula used to convert gas meter readings to kilowatt hours (kWh):

Electricity meters usually show the amount of electricity you have consumed in kWh and the provider bills you directly for that usage. However, gas meters cannot show the amount of energy you have consumed, just the amount of gas which has passed through, either as HCF (hundred cubic feet) or cubic meters if you have a metric meter. For billing purposes this has to be converted to kWh by a formula. A key element of this formula is the Calorific Value of the gas, which is a number relating to the amount of heat you will obtain if a certain amount of the gas is burnt. This number can change daily, but generally has a value between 37 and 44 and variations to it will only make a small difference to your gas bill. If you really want more information about it you might want to look here: http://www.nationalgrid.com/uk/Gas/Data/misc/reports/description.
The formula used to convert meter readings to kWh is generally printed on your bill, but the formula used on this site on the costs pages is as follows:

Take the units used as reported by the meter
Multiply by the metric conversion factor (2.83)
Multiply by the volume conversion factor (1.02264)
Multiply by the calorific value (currently 39.47333 - region not specified )
Divide by the kilowatthour conversion factor (3.6)

So, a consumption of 1 unit on an imperial meter would currently equate to 31.73 kilowatthours on the mycosts website.

Click here for a unit to kWh conversion.