We convert gas units from your meter into kWH to make sure the energy output is priced consistently. We do this by using this formula.
How is my gas usage calculated?
For metric meters:

Multiply by volume correction factor (1.02264).

Multiply by calorific value (as shown on your statement).

Divide by kWh conversion factor (3.6). = Energy Used.
For imperial meters:

Convert from imperial to metric by multiplying the units by 2.83.

Multiply by volume correction factor (1.02264).

Multiply by calorific value (as shown on your statement).

Divide by kWh conversion factor (3.6). = Energy Used.
Will there be any changes to how gas is calculated?
Natural gas is metered by volume and its energy content varies with its pressure, temperature and calorific value. The composition of the gas also changes slightly from time to time, which means that the calorific value (energy content per unit mass) will also vary.