Gas is recorded in m3

Smart Meters only report gas consumption in m3 (cubic metres) and not kWh, this means you'll need to convert m3 to kWh to calculate energy consumption.

To convert from m3 to kWh requires knowledge of the calorific value (CV) of gas at that time and for the location of the gas meter. CV values range from 37.5 MJ/m3 to 43.0 MJ/m3. Different organisations use different approaches to calorific values (taking the daily values issues by national grid through to weekly, monthly or longer averages per region or nationally, some also use a fixed figure of 40 in their calculations). As a result we can not reliably calculate the kWh for you, therefore n3rgy has decided to allow you to make the decision on which to use in your calculations. The simplest mechanism is to use the following formula replacing CV with a fixed value of 40

(m3 x 1.02264 x CV) / 3.6 = kWh

m3 = cubic metres of gas for conversion
1.02264 = Volume Correction Factor defined by GB Government
CV = Calorific Value, typically 40 but you can find more accurate numbers via the national grid link below
3.6 = To convert from MJ per m3 to kWh

More information on Calorific Values and daily values can be found at:
https://data.nationalgas.com/find-gas-data 

If you'd like to understand more about the details and thinking behind gas calculations, this blog is helpful
http://paullewismoney.blogspot.com/2018/05/why-your-gas-bill-is-wrong.html