How to calculate gas and electricity usage


Im sure this is a very simple thing for most people but I am completely confused by all the numbers

Having read an article in the week about energy companies ripping customers off and bills not being clear I thought I would just double check ours as to be honest I just let the direct debits take care of themselves

We did a reading ourselves a year ago and then another reading was taken by the meter reader in the summer but I am only going by last October's reading as that gives me a years overview

So electricity shows a useage of 5100 (when you take the reading from last year away from this year)

I take it,, that this is 5100 kilowats?

But the gas is harder to fathom, I work it out as 861 useage. But no where on the bills Ive downloaded are these numbers? It says that our estimated usage is just under 20 000 kilowats a year, 861 is no where neaer that. Plus when I just put in the new gas reading just now it said to check again as it looked very high.

Does anyone know what 861 means for the gas usage, is that the same as 20000 kilowats?

We were paying £134 per month for a small 3 bed semi which I thought was rather high, but having put our new readings in, it has put us in quite a lot of debt so I think the bill will now go up even more!

We are with eon and its gas and electric together


Well-known Member
Electricity should be fairly straight forward as the meter will record kWh directly, so providing you are using actual readings (rather than estimates) you can simply multiply the kWh consumption by your unit cost (shown on the bill as pence/kWh) and that’s the part of your electricity bill related to consumption. You will also pay a standing charge, usually shown in pence/day, so you can simply multiply this by the number of days you are calculating your usage over, and you now have the two elements of cost that make up your electricity bill.

Gas is a bit more complex as the meter measures volume - older meters record in 100s of cubic feet, and modern meters record in cubic meters. This then has to be converted to kWh using various conversion factors (again shown on your bill). So once you have the average conversion factors to convert your meter readings into kWh you can then continue with the cost calculations as you would for electricity.

Going forward, for accurate bills, you need to make an effort to supply meter readings regularly, but also check that these readings are also being used for your bills too. If that is difficult then you should consider smart meters as these should ensure your bills are always based on your actual consumption, and the in-home display that goes with them will also show both consumption and cost data too, making it easier to follow.

The only other reason for bills being inaccurate is if the direct debit charges are way off for your actual consumption, so again, knowing how much you use and the pattern it follows can help you check you DD payment is roughly correct based on your previous history.


Well-known Member
Does anyone know what 861 means for the gas usage, is that the same as 20000 kilowats?

If that is 861m³ then according to my formula:

Calorific Value=39.2
Volume Correction=1.02264

(861 * 39.2 * 1.02264)/3.6 = 9588kWh

Using an online calculator:

86100cft is 25233kWh


Thank you, that does seem high, we rarely have the heating on though as we have a wood burner

This is now quite puzzling


Well-known Member
Apologies if I'm stating the obvious but gas prices have shot up in the last few months so if you're on a variable tariff that could explain it.


You're right but It was more that we put a new reading it and as it said to us when we put the reading in, it seemed really high. Not sure why, last reading was done in the summer. Perhaps Im feeling the cold more these days but thats not like me


Well-known Member
But no where on the bills Ive downloaded are these numbers?

Check your bill again, these were from two different suppliers and I'm sure all bills have this information.

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