Blazers (or Sport Coats):
Figuring your jacket size is the simplest lesson ever. Basically, you calculate your chest size by literally wrapping a measuring tape around the fullest part of your chest (typically, under your armpits). If you measure 40 inches around your chest, then your chest size is 40 inches and, likewise, your suit jacket size is 40. As long as you're honest with yourself, this should be easy enough!
- You are 5’9” and your chest is 40 inches around, your jacket size should be 40R.
- You are 6’3” and your chest is 40 inches around, your jacket size should be 40L.
Makes sense so far? Great!
The most important thing to know is: DO NOT base your dress pant size on your jeans size. Why? Jeans and casual pants are vanity sized (not to mention the fabric has more stretch). Just because they say they are a size 34 does not mean they actually measure 34 inches around.
The best thing is to physically measure the waistband of a pair of dress pants or slacks that fits you well and sits at your waist (not lower, like jeans are often worn). If you don’t have any dress pants, measure your actual waist (just above where you’d wear your belt). Jeans and casual pants can be worn on the hips, but, trust us, dress pants are the most flattering when worn on the waist.
Once you have measured your waist or the waistband of your favorite dress pants, that number is your pant size. So, if your waist is 34 inches around, your pant size is 34 or 34W (W stands for waist), depending on the manufacturer tag.
Don't sweat the sizing too badly. Manufacturers think ahead and include extra fabric at the waist and seat in case the pant needs to be let out (up to two additional inches). Pants can also be taken in, up to two inches, as well (there are also slim fit pants available).
Pants also come with an inseam measurement. This represents the inner seam of the pant leg, from the seat seam below the zipper down to the bottom hem. Pants can be purchased unhemmed or pre-hemmed (in this case, it will have two numbers separated by an ‘x’ (e.g. 34x32)). That second number is your inseam measurement.
There are many different styles that can be expressed by inseam length, but that’s a story for a different day. All you need to know is that, in traditional men’s tailoring, most dress pants should hit the back of your dress shoe and have a small break in the front.