What's the equation to convert gas meter readings into kWh?

Hi @Johnnyhornet 

First the easy one. The electricity should be measured in kWh on the meter. So to work out how much you’ve used since the last reading you simply take the old reading away from the current reading on the meter.

Now for the trickier one (science books at the ready)…

Gas meters can measure usage in cubic feet or cubic metres. If yours is measured in cubic feet then multiply the value by 0.0283 to get cubic metres.

The volume of a gas is dependent upon pressure and temperature and therefore varies. The volume of gas measured by the meter is adjusted by multiplying by a correction factor to take account of the temperature and atmospheric conditions. The correction factor used will be shown on your gas bill (e.g. 1.02264).

Next, the volume needs to be converted into a calorific value (CV) which is a measure of the energy released when a given volume of gas is completely combusted. This depends upon the gas’s composition. The CV usually ranges from 37.5 to 43.0 MJ per cubic metre. The value used should also be on your bill.

Finally. the thermal energy can be converted into kWh. 1 Watt is 1 Joule per second. 1 Joule is 1 Ws. 1 kWh is 1000x3600 Joules = 3.6 MJ.

So divide the CV by 3.6 to convert MJ into kWh.

There will be a test next week, so don’t forget to revise.