Do not follow the "size up" advice.

My husband wears a 11.5 D. I ordered a 12 based on the reviews here. The shoes are HUGE. He should be in an 11 if not a 10. In fact, he fell while wearing these shoes. Wore them three times and fell due to the poor fit. Needless to say, he does not have these clogs any more.

Don't size up. In fact, if you have normal sized feet, I'd suggest looking at another brand of synthetic clogs.