How To Measure Mens Chest Size For Jacket. Measure from the edge of the left shoulder across the back of the neck continuing to the edge of the right shoulder. To find out your chest size, take a tape measure and wrap it under your armpits at the fullest part of your chest.
If you want a loose fitting jacket, always go for +1 size. Ideally ask your mum, spouse, or best friend, to wrap the tape measure around your chest area. For full measure double the posted measurements.