Each wrong answer costs 5 points
100 ÷ 20 = 5, so a 20-question quiz has only 21 possible scores, all whole multiples of 5: 100%, 95%, 90% and down to 0. That makes the percent easy to work out in your head: count the wrong answers, multiply by 5 and take it off 100. It also means rounding never changes a grade on 20 questions, because no score lands on a fraction of a percent.
Letter grades out of 20
On the standard scale an A is 18 to 20 right (up to 2 wrong), a B is 16 or 17, a C is 14 or 15, a D is 12 or 13, and 11 or fewer is an F. Every letter covers just two scores, so a single extra mistake moves a student from 90% (A) to 85% (B).
Why some plus-minus grades never appear on 20 questions
With 5-point steps, a 20-question test skips whole bands of the plus-minus scale. An A+ starts at 97%, and the only score above that is 20 out of 20. B+ (87–89%), C+ (77–79%) and D+ (67–69%) fall between two possible scores, so nobody gets one: 85% is a B and 90% is an A−. If your gradebook uses plus and minus letters, a quiz of this length can only ever give A+, A, A−, B, B−, C, C−, D, D− or F.
Example: a 20-question quiz with 3 wrong
3 wrong is 17 right. 17 ÷ 20 × 100 = 85%, a B on both scales. To grade a quiz that also has extra credit or half points, use the grading calculator; for a single score with odd point values, like 17.5/20, the percentage grade calculator.
Where the letter lines come from
The A–F column uses the standard scale that the School District of Palm Beach County and Roanoke County Public Schools publish: A 90–100, B 80–89, C 70–79, D 60–69, F below 60. The +/− column uses A+ from 97, A from 93 and A− from 90, and so on down to D− at 60. Schools set their own lines, so check your syllabus; the grading scale page compares published scales. Other test lengths: the grading chart for 1 to 100 questions.
20-question grading questions
What is 17 out of 20 as a grade?
17 out of 20 is 85%: 17 ÷ 20 × 100. That is a B on the standard scale (B from 80) and a B on the plus-minus scale too, because 85 sits between 83 and 87.
How many can you get wrong on a 20-question test and still pass?
Eight. 12 out of 20 is 60%, the lowest D on a scale where D starts at 60. With 9 wrong the score drops to 55%, an F. If your school passes at 65 or 70, the limit is 7 or 6 wrong.
What is 15 out of 20?
15 out of 20 is 75%, a C on the standard scale and a C on the plus-minus scale (73 to 76). Five wrong answers cost 5 points each.