Chest: The jacket size is to fit the chest measurement as shown. Measure around the fullest part of your chest (the full circumference, keeping the tape well up under your arms and across the shoulder blades).
Length: This is the length of the jacket down the centre of the back from the nape of the neck to the hem.
Waist: Measure around your waist (over your shirt, not over your trousers) at the position where you normally wear your trousers. Keep the tape a bit loose, so it is comfortable.