1. Measure your waist, around your natural waistline, just under your rib cage, and note down the number in centimetres or inches.
2. Then measure your chest as shown, around your fullest part, with the tape under your armpits, making sure the tape is flat across your back.
3. Check where your measurements fall on the charts below, either in centimetres or in inches. That will be your size.
4. Or if you like, you can use your chest size for comparison to select your size using this chart in red.