According to Official Guinness Records,
The largest sand dollar measures 14.8 cm (5.826 in) at its smallest diameter and was found by Dan Manna (USA) in Holmes Beach, Florida, USA, on 11 May 2013.The sand dollar measures 16 cm (6.299 in) at its maximum diameter and weighs 153 grams (5.4 oz).
For a complete list of 2013 records, please visit 2013 Guinness Records in United States.