Just as you would fit yourself properly in a suit jacket or blazer, you would do the same here except for the obvious - fit into a coat a size larger than your suit jacket or blazer. This would mostly apply to over coats and particular trench coats. Remember, the cool thing about pea coats and trench coats, specifically, is that you can wear them dressed-down or dressed-up. As long as the weather calls for it, don't be shy to get different styles of coats for different occasions in both casual and formal. Another note, gentlemen, all the items you see here (like any other post) are samples of fashion that are in trend. This doesn't mean you have to go out of your way to hurt your wallet to get the right coat. Sure, quality is very important, but it has never been about the labels. If you have the currency, then go ahead and do what you have to do. For the other gentlemen that wish to make an investment, make sure the fit is right and try picturing using that specific coat with different outfits, regardless of how much it shows on the price tag.