Hi Rosaeleena.
I managed to pick up this Fab Fendi belt from Net a Porter last week, they only had a size large left, but I was so desperate for one that I thought oh well, I can always have my shoemaker put another hole in it if necessary.
Fat chance!! the belt is designed to sit right in the middle of the waist, and definitely not on the hips. My belt states that it is large and also has 34" written inside it, but I measured it and its 32"!!
I am a uk size 10-12 and have a 29" waist, and the large is perfect for me!
So, in theory, the small would be 26 to 28", the medium would be 28-30" max, and the large is for 30-32", but it is very very tiny, so assume you need the next size up if you are planning to get one, and if you are looking for a belt that you can also wear low with jeans, it is not this one!!
hope that helps x