21/64 as a Decimal 0.328125 21/64 = 0.328125 = 32.8125% Copy 21/64 = 0.328125 = 32.8125%. Formula Used21 ÷ 64 = 0.328125 Frequently Asked Questions What is 21/64 as a decimal?0.328125.What is 21/64 as a percentage?32.8125%.