My son had J1 size which started to be small, so i ordered these in J2. They were just slightly larger then J1. This shoe was not available in J3, so i had to order different type of crocs. We have been using crocs since my son was 2 years old and the sizing was a large difference between 12/13 and J1...so i expected J1 to J2 to be a full size up but it is just 1/2 size.<br /><br />5 stars are for shoe design. All the air holes make the foot sweat less and let the water out easily.