Sizes: The ear band has a Velcro fastener at the back, thanks to the upgrade Velcro fastener, the band can be flexibly adjusted for a larger area of head circumferences. M: 54 cm / 21.2 inches with a head circumference of about 36-46; L: 58 cm / 22.8 inches with a head circumference of about 42-50; further settings before swimming, fits perfectly into the respective ear.
If the head circumference is between 42-46, size M will be slightly tighter and size L will be slightly loose.