Hello, we recommend that you measure your wrist circumference as in the image to find the size that best suits you. Standard size (M-L) fits people who have 15.7cm to 18.5cm wrist circumference. The Junior size (XS-S) is suitable for people with a wrist circumference of less than 15.7 cm. To generalize, size XS-S fits most children and women, and size M-L fits most men over the age of 15. If your wrist circumference is greater than 18.5 cm, we suggest you look at the stainless steel models, which are priced higher. Because the stainless steel models have adjustable straps, they fit 99% of all wrists, just like watch bands.