Sharkbanz are designed for one size fits all, and a universal fit for ages 5+. After sizing to your preferred ankle, any excess band slack can simply be cut with a regular pair of scissors.
Sharkbanz 2 units will comfortably and securely fit ankles up to 13" inches in circumference. The best way to find out for sure is to measure the circumference of the wrist or ankle with a tape measure. If it’s between 5.5 and 14 inches (14 and 35.5 cm) then you're all set!