These fins keep fitting growing children through to adult size, most likely with regular straps. So, you don't need to keep buying new foot fins every time your shoe size changes. If you are still growing, these fins will keep fitting you. They fit regardless of foot size and shape. The fin centre flexes inwards to fit younger, thinner legs and flexes outwards to keep fitting as you get older and your legs grow larger. The one size easily fits everyone taller than about 140 cm (4 feet 7 inches) up to very tall people. They actually still fit if you are a bit shorter than this, but they may stick out a bit more from your toes. Swimming with them is still fine. Walking might be a bit harder but will get easier as you grow. The regular straps fit most people up to large adult size. The straps go around the narrowest part of your leg, just above your ankle. If this circumference stays within the range 20-40 cm (8-16 inches) then the regular straps will keep fitting you. But if you expect that this circumference will become larger than 40 cm (16 inches), then just select the option for longer straps when you order your fins. Or you can order longer replacement straps later if you need them.