What is 40% of 20? 8 40% of 20 Copy 40% of 20 = 8. Formula UsedResult = (40 ÷ 100) × 20 = 8 Frequently Asked Questions What is 40% of 20?8. (40 ÷ 100) × 20 = 8.How to calculate 40%?Multiply by 0.4 (or multiply by 40 then divide by 100).