Around 1 million imperial meters are replaced with metric ones every year. Here's a guide to find out if you are being billed correctly against the type of meter you are using.

On Watchdog 12 January 2008 we showed how a mix-up with two different types of gas meter, has led to customers being overcharged by thousands of pounds. The mix-up typically occurs when older imperial meters are changed to modern metric ones. For some reason, in a number of cases, the energy supplier has not recognised the meter changes when calculating bills.

## A step-by-step guide to checking your gas bill and meter

Gas bills from the energy companies aren't particularly easy to understand and each supplier prints bills in a slightly different way. Checking to see if you're being billed correctly therefore, isn't exactly straightforward.

The only foolproof way of checking if you're being billed correctly is to follow a series of steps, and do a basic calculation.

### Step 1

Check that your gas meter's serial number, matches the meter number shown on your bill. The number will often be somewhere in the small print of your bill. If the serial numbers don't match, you could well have a problem and you should contact your supplier to check they have the right information.

### Step 2

Check what type of meter you have.

Imperial meter

If it is an old imperial meter, measuring gas in cubic feet, it will probably have the words 'cubic feet', or the letters 'Ft' shown somewhere on the front.

Metric meter

If it is a newer metric meter, it will probably say it measures gas in 'cubic meters', or will have the letter 'M' on the front.

### Step 3

All energy bills are priced in kilowatt Hours (kWh), so your supplier has to do a calculation to turn the numbers on your gas meter (units) into kWh's. The only reliable way to see if they are billing you for the correct type of meter, is to do the same calculation.

This calculation differs, depending on whether you have an imperial meter or a metric meter.

Before starting the calculation, you need to find the following numbers, which differ depending on your location, but should always be printed in the small print of your bill.

• The metric conversion factor (for imperial meters only)
• The volume correction factor
• The calorific value of the gas

Imperial calculation - if your meter measures in cubic feet:

To convert the readings on an imperial meter from imperial units to kWh's the company should do the following calculation;

(The number of units you've used) X (The metric conversion factor) X (The volume correction factor) X (The calorific value of the gas) divided by 3.6 = kWh's.

The number of kilowatt hours you calculate should match the number of kilowatt hours the energy company says you've used. If they don't, then you should query your bill with your energy supplier.

Metric calculation - if your meter measures in cubic meters:

The metric calculation is similar to the imperial formula, with one important exception. Because a metric meter already measures in metric units, it doesn't need a metric conversion factor. Therefore this part of the calculation isn't required.

The correct calculation is:

(The number of units used) X (The volume correction factor) X (The calorific value) divided by 3.6 = kWh's

The number of kilowatt hours you calculate should match the number of kilowatt hours the energy company says you've used. If they don't, then you should query your bill with your energy supplier.