There is a metallic plate within the sash of the window on the top right hand side which features a long code. We work using that code because it provides easy product identification and has details of product type, dimensions and production code.
You'll notice the ID plate may say 78/118 or 114/118 for example and this is the size you will need to look for. On RW4U the sizes are listed as 78x118 etc so please search for that term.
Often we have queries about the glass measurements and if that's how you know what size to order. Unfortunately this method is incorrect. Measuring the size of the glass will give you the wrong measurements therefore causing problems for your order as it'll come across as a bespoke size.