Can anyone clarify why some shops sell 50mm thick studs, while others sell 38mm ones? I'm having a hard time finding explanations for this. Some sites even list both sizes!

Image of advert showing single item with two different sizes in description

I need to build a stud wall on my existing brick party wall and been told to use 50mm and I don't know what to buy now. :)


Timber is dimensioned in 'nominal width' which means the size it is sawn to when it's processed. Studs are finished by planing, which reduces the nominal width to the actual physical width you'd measure when you installed it.

This webstore's description makes a bit clearer. It specifies that a nominal 50x75mm stud is reduced to 38mmx63mm by planing to produce a smooth surface.

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UK timber sizes are usually the direct metric equivalent of traditional imperial measurements. In your example 50x75mm is a 2x3 (two by three).

Traditional timber sizes were nominal sizes. These were notionally something like the sizes of the first rough cuts from the logs. Since timber shrinks as it dries, and when planed smooth, the actual dimensions are usually significantly smaller. For example a 2x4 might measure roughly 1¾ x 3½

In your case, 50mm is the thickness and is unlikely to be a critical dimension.

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