LavnisMen's Trench Coat Long Wool Blend Overcoat Slim Fit Down Topcoat

Is American size ?

Hello. I wear between a 42-44 size suit. 34 waist. 6 ft 1. 205lbs. What size is best? Normally wear large but most reviews are saying go up one size..

What are the exact measurements of each size? Are these Chinese sizes or American?

Where can I get a replacement button?