Measure around the fullest part of your chest, keeping tape firmly under your armpits and around your shoulder blades.
Measure around your waist, slightly below your natural waist, where you normally wear your trousers.
Measure around the fullest part of your hips.
Measure the length of your arm, from nape to low shoulder point, then down to the wrist bone.
If your measurements are in between those listed in the size chart, pick the next larger size.