I am a size 16 collar
How would you translate the phrase above into Russian? (the man is buying a shirt)

That sounds a bit peculiar that the person says the collar size; are there any other common ways to denote the size of a shirt in GB? Or can you, for example, just say 'I am a size 16.' in this situation?So, I found out that it is translated размер по вороту. In Russia it is the same, actually. I just never happened to buy a classic shirt.

Question

I am a size 16 collar
How would you translate the phrase above into Russian? (the man is buying a shirt)

That sounds a bit peculiar that the person says the collar size; are there any other common ways to denote the size of a shirt in GB? Or can you, for example, just say 'I am a size 16.' in this situation?So, I found out that it is translated размер по вороту. In Russia it is the same, actually. I just never happened to buy a classic shirt.

Answer

Men's shirts are always sold according to collar size in Britain. In the case of casual tops and T shirts, they might be S, M, L - small, medium and large - with 'extra small' XS and 'extra large' XL - or even XXL - as additional sizes at either end of the scale.

Size + a number is a woman's dress size. A (largish) woman would say 'I'm a size 16', but a man wouldn't say this. He might say 'I take a sixteen inch (collar)'. 
Sixteen inches is 41 cm, which is an average/medium size.

Answer

Yes, in Britain, men's shirts are always sold according to collar size.  The 16 in your example refers to inches.  "I take a 16" inch collar."  "I am a 14 and a half."   Collar size gradation is by the half inch.

Shirts made in Italy are sold by the collar size as well, but measured in cm.  A 16" collar shirt is known as a size 41 shirt.