For closed-back styles (Loafers & Smoking Shoes)... It’s a perfect fit if initially they feel snug (even uncomfortably so), but your toes are flat rather than scrunched up to fit.  Much like high quality leather shoes, our Kilim shoes will stretch to mold to your foot. They are too large if you can fit your finger in the space behind your heel. They should be exchanged for a smaller size.  If there is just a bit of space, and your heel occasionally pops out of the back, a heel insert (available on Amazon.com) may do the trick. They are too small if your toes are curled under to squeeze into your Kilim shoes lengthwise, or if the tips of your toes are jammed against the very front.  If your toes are flat but the shoe is very tight around the sides of your feet, hang in there! The Kilim material will stretch to accommodate your foot width-wise and a tiny bit lengthwise. For open-back styles (Slides, Slippers, and Mules), the length is really personal preference. Some customers prefer for their heel to hit right at the edge of the shoe, and others like a little more space behind the heel--as long as your comfortable and like the look, it's a fit!