18/20 as a Decimal 0.9 18/20 = 0.9 = 90% Copy 18/20 = 0.9 = 90%. Simplified: 9/10. Formula Used18 ÷ 20 = 0.9 Frequently Asked Questions What is 18/20 as a decimal?0.9.What is 18/20 as a percentage?90%.