Let's start with the simple. To find underwear, simply use the same system that we show you in the clothing size section. It's quite simple, you just have to measure yourself with a tape measure around where you put on your underwear. Next, go to the conversion table and see what size corresponds.
For bras, you can also use the tape measure if the measuring system of cups is not the one you use in your country. Then you should measure (the bust at 45 degrees to determine the size of the cup and the bottom of the breasts to determine the size of the band):
For socks, simply follow the steps shown in the shoe section. Sock sizes work the same as shoes. The only difference is that they go by ranges, since, for example, the number 39 for the European 42 is the size M (if my foot number is between this range, then I would buy M stockings).