I usually wear a size 11.5 to 12 shoe.  Since these are slip-ons, I wanted to get them a little tight so that they would still fit once they broke in.  So I got a pair of 11.5 and my feet were swimming.  No worries; free exchange with Amazon, and a few days later the size 11 arrived.  They are a good, comfortable, casual work shoe.  I would just recommend buying at least a half size small… maybe even a full size down.<br /><br />UPDATE:  After 1.5 years, and good performance, I ordered another pair.  I thought I had already dialed in the size with the last purchase.  The second pair was WAY too big.  Very disappointed by the apparent lack of uniform sizing.  The same shoe 18months later was completely different.