Please measure around your chest as shown in this diagram.
Once you have your chest measurement.
please choose your size from the table below.
If you are using US or EU sizes, these Vests are larger than standard.
so order 1 size below your usual size.

Chest Measurement Men's US US Women EU Women Order Size
under 37 Inches S 4 8 XS
37-40 M 6 to 8 10 to 12 S
40.5-44.5 L 10 to 12 14 to 16 M
43-47 XL 14 to 16 16 to 18 L
46-50 XXL XXXL 18+ 20+ XL