Listen to the other reviewers and buy a size down.  I usually wear a size 11 sneaker and my previous Clarks slip ons were size 11.  I ordered size 10.5 and even that was too big.  I returned and bought a size 10 and they felt tight for about 2-3 hrs.  They are now warming up and streatching to be very very comfortable.  I only gave it 4 stars because I feel shoes should be better made in general and cheaper.  Seriously, its a piece of rubber with dead cow.