I agonized over which size to order and found it very confusing that many reviews said the slim Havaianas fit true to size.  I wear a 9.5 consistently in shoes and go up to a 10 when there are no half sizes.  After reading hundreds of reviews and checking out every size chart I could find, I ordered the 9/10. Big mistake.  They fit a whole size too small.  There was no way I could have worn them.  I don't understand how these fit true to size for anyone.  But the returns process was very easy so that was a relief.