Gas Meters read in Cubic Feet or Metres... not kWh:
Your gas meter will show a reading in Cubic Feet (old style) or Cubic Metres (modern) and your meter should state which type it is, but your energy bill will be shown in kWh (kilo-Watt-hours). To get a meter reading to show how many kWh you have used, here is the formula they use:
1. Get the Current Meter Reading. You will of course need to know what your previous reading was in order to calculate the usage, eg 1234.567 (prev) 1244.123 (current) is therefore 9.667 units used.
2. If your meter is an old one, that will be Cubic Feet so you need to convert this to Cubic Metres first, to do this, divide the value by 35.32, eg 9.667 / 35.32 = 0.2736 Cubic Metres or CM. This is the value that your bill will be calculated on. We'll assume our meter is showing in metric and so no conversion is needed, ie our 9.667 units used.
3. Gas has a Calorific Value, that is what the 'energy' of the gas actually is and this is a pretty stable value as your provider needs to keep it this way because most gas appliances need to work on a fixed energy rating. This value is typically 39.7 and can be seen on your bill. Multiply the Cubic Meters value to get the new value needed, ie 9.667 x 39.7 = 383.779
4. We now need to adjust the value for 'Volume Correction'. Like the calorific value, this is pretty constant and the value used is 1.02264 and so 383.779 x 1.02264 = 392.469
4. You now need to get the final Cubic Metres volume of gas value into the actual kWh used. This is a simple calculation, just divide the volume of gas used by 3.6, ie 392.469 / 3.6 = 109.02kWh
5. Now we have the kWh, you need to multiply this by the rate your provider has given you on your tariff. Currently this may be capped but lets assume you pay 35 pence per kWh. In this case, your gas used bill would be £38.16 (plus VAT)
Summary:
Multiply the: Units Used x 39.7 x 1.02264 and then divide the result by 3.6 to get kWh
or for a 'quick and dirty' just use Units Used x 11.278
Don't forget, you need to add your Daily Standing Charge and then add 5% VAT to get the value you will actually need to pay.
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