Finding out how much gas and electricity you use, on average, each month is key in being able to switch to a deal that will save you money - the more accurate you can be, the better.
The easiest way to find out is by checking your annual energy statement. Alternatively, check recent utility bills - as many as possible. You'll need to base your calculations on the Kilowatt/Hour usage figures rather than the cost - your supplier should be able to give you this information if you're unsure. You'll also need to check whether your utility bills are issued on a monthly, quarterly or annually basis.
If they're issued annually then you'll simply need to divide the total kw/h by 12 to get your average monthly gas and/or electricity usage.
If your bills are issued quarterly you'll need to divide the total by 3 to get your average monthly usage.
And, if your gas bills are issued monthly, you'll need to add together total usage figures for several months and then divide this by the number of months included.
As the amount of gas and electricity you use is likely to vary substantially over the course of the year, it makes sense to add together totals from as many monthly or quarterly utility bills as possible before working out an average.