How to I tell the physical size of my hard drive?

I want to buy an enclosure case for my old hard drive, but I don’t know what size it is.
It came with (in) my old desktop dell computer.

It seems most hard drives are 2.5" or 3.5", I guess 2.5" being for laptop and 3.5" for desktop, is this correct?
If so, can I then assume that my hard drive is 3.5" and buy a 3.5" casing for it?

Edit: sorry about the typo in the title, I meant “do” not to…

Welcome to HWF :slight_smile:

All desktop hard drives are 3.5", because 2.5" drives can’t be mounted inside the case.