Posture Corrector Size Guide:
Take a tape measure (or string if you don't have one), and measure the circumference of your chest from right under the armpits going all the way around.
Choosing a size based off your chest size is recommended as this will be more accurate.
Extra Small: 18-26 inches / 46-68cm (chest size)
44-88lbs / 20-40kg (weight)
Small: 27-36 inches / 68-91cm (chest size),
88-176lbs / 40-80kg (weight)
Medium: 36-47 inches / 91-119cm (chest size)
154-220lbs / 70-100kg (weight)
Large: 47-59 inches / 119-150cm (chest size)
176-264lbs / 80-120kg (weight)