Checking for the correct measurements

Checking for the correct measurements
19th October 2017 Swtch

Our product pages will tell you if the switch or socket in question fits a standard UK back box. This information is shown when you click the “Dimensions” toggle box, below the main product information (pictures, price etc). But it is always a good idea to double-check before you order your new switches! Here is how:

If you are planning to replace an existing switch

Before you can measure the width and depth of the back box, you need to detach the existing switch or socket off the wall to inspect the box. You usually don’t need to actually disconnect the unit, but since you are exposing wires always make sure that the power supply is switched off at the consumer unit.

You then need to remove the faceplate/switch. How you do this depends on the type of switch you have – it could be that you need to loosen a couple of screws or pull off a decorative screwless plate first.

We find these instructions for the whole process of changing a light switch really useful: Web version, PDF download

If there isn’t a switch installed

Much easier! Just measure width and depth of the empty back box.

If there isn’t even a back box yet

If you’re at the planning stage or want to add a switch where there wasn’t one previously, just follow our recommendations about using round Euro back boxes like this one for dry/hollow walls. They give you the most flexibility in choosing one of our products, like these beautiful retro numbers with round backplates for example.


UK metal back boxes (or “knockout boxes”) are usually 72mm square, give or take a couple of millimetres. Dry-lining back boxes made of plastic have an inner width of 70mm and a small lip that sits on the wall.


These are the most common back boxes sizes in UK homes. Check on the relevant product page, but in general it’s best to have a box that’s at least 35mm deep, to give you enough space for the slightly deeper European inserts and the wires.


Non-standard boxes

In some cases you might find other back boxes (made from wood, for example!) or the back box will be partly covered by excess plaster. If that is the case, measure the width of the opening and compare it to the information in the “Dimensions” section of your chosen product’s page. The diagram of the product shows the size of the insert part of the switch/socket. In this example it is 52mm:

As long as the insert fits into the opening and the screws that hold the insert are accessible, you should be fine.