How is gas consumption calculated?

If you are connected to the natural gas network, perhaps you have already noticed that your gas bill is based on the kilowatthours (kWh) that you have consumed, whereas your meter measures the cubic metres (m³) delivered to you.

Converting m³ into kWh guarantees that you receive a fair, accurate bill, where you only pay for the energy that you have actually used. The calorific power of the gas, i.e. the amount of heat it can produce, varies according to several factors.

In addition, two types of gas exist side-by-side in Belgium:

• rich gas with high calorific power
• lean gas with low calorific power: this is the gas available in Brussels

All Belgian consumers will have rich gas available from 2023. The differences in calorific output will therefore be less, but will not disappear for all that...

How are the m³ of gas delivered converted into kWh?

The volume (read on the meter) is multiplied by the mean value of the energy potential of the gas during the period in question. Your network manager, Sibelga, performs this calculation.

One m³ of natural gas contains between 9.5278 and 12.7931 kWh depending on its type. In Brussels, this figure currently fluctuates around 10 kWh/m³.

This value is constantly recalculated to ensure that the bill is fair. Natural gas, as its name suggests, is a product of Nature and not a manufactured product. Its composition can therefore vary depending on its geographical origin. Belgium receives gas from several regions in the world. In addition, the energy content of the gas varies according to the height above sea level of the place where it is consumed.

When all Belgian consumers are supplied with rich gas, this conversion calculation will still be necessary with an annual mean value recalculated constantly.

The exact conversion factor is shown on your bill and is accurate to four decimal places. You can check whether there are slight year-on-year variations.

How is the amount of my gas bill calculated?

Your annual natural gas bill is drawn up by your supplier in three stages:

1. The difference is calculated between the current index (in m³) and the index from the previous year. The result gives the volume of gas delivered to you, expressed in m³
    
2. This figure is then multiplied by a conversion factor to express in kWh the amount of energy that you have actually consumed.
    
3. To establish your bill, your supplier multiplies the number of kWh obtained by the price per kWh of the rate you have chosen via your contract.

Sample gas consumption calculation

Gas meter reading:
January 2017: 27 000 m³
January 2018: 29 100 m³

Annual consumption: 29 100 m³ - 27 032 m³ = 2100 m³

Equivalent in kWh: 2100 m³ x 9.9 kWh/m³ = 20 790 kWh

Your supplier multiplies this figure by your contract rate (about €0.06/kWh):
20,790 kWh x €0.06 = €1,247.40