The size is M, and I think it's about 24cm. I usually wear 23cm to 23.5cm, but these shoes were a little big on me. I've only worn them in the entryway of my house, and they've been stored for a long time. The instep strap has Velcro, so you can adjust it to your preferred position. The shoes are also wide, so they're comfortable for people with high insteps or wide feet. The jewel on the instep strap is a 2-way design that can be removed! You can attach both for a glamorous look, or remove them for a clean, simple look.