This strap is crafted from soft, genuine leather to add elegant, timeless style and undeniable strength, making it the perfect piece for wearing when you want to elevate your look after your workout. As it's more of a fashionable accessory rather than a sporty one it's important to note that the leather is neither sweat nor water resistant, so it's important to limit its contact with moisture to reduce discolouration and damage. Sizing: Small - Fits wrists 14-17cm in circumference Large - Fits wrists 17-20.6cm in circumference Please note: This is just the strap, you'll need to buy the Fitbit Alta Wireless Activity and Sleep Tracking Smart Fitness Watch separately.