As said above, both utilities are charged for in kWh. Electricity meters measure in kWh but gas is measured volumetrically, not in the energy value (although there is no reason why it couldn't make the conversion and display it directly, typical opacity and/or lack of imagination). If your gas meter is very old it will measure consumption in ft³ but most meters nowadays measure in m³. You need to convert the gas reading accordingly, the two volumetric units obviously go through two different conversions.