Sizing was difficult...I take a UK size 5 (EU 38) but the slider sizes appear to be 3.5; 4.5; 5.5, etc. I purchased the 4.5 (I initially bought 2 pairs of different colours so that I could have a comparison). The pink 4.5, we're too big as the strap over my foot was 'baggy'.... The black pair, of the same size, we're more of a snug fit across my foot but (like the pink ones too) the sole is about one-inch/3cm too big! Given that I guess the 3.5 would be too small I ended up buying the black pair but I would have preferred the sole to be a better fit! I have now worn my black Nike Victori Sliders and although being slightly self-conscious of the 'too-big sole'; I am happy with them. I wore them indoors; walking too and from the changing rooms to the swimming pool and then for the duration of my shower (in the swimming-pool public showers).