Education guide
What Is 18 Out of 30 as a Grade? Test Score to Percentage Charts
18/30 is 60%, a D−. Score-to-percentage and letter-grade charts for tests out of 10, 20, 25, 30, 40 and 50 — plus the rounding rule that turns a B into a B+.
By M2Toolkit Editorial TeamPublished 6 min read
Quick answer
18 out of 30 is 60%, which is a D− on the common US scale — the lowest passing grade. One more correct answer (19/30) makes it 63.3%, a D. One fewer (17/30) is 56.7%, an F.
For any score: divide the marks you got by the marks available, then multiply by 100. The charts below do that for tests out of 10, 20, 25, 30, 40 and 50.
A raw score like 18/30 or 34/40 doesn't tell you much until it's a percentage, and a percentage doesn't mean much until you know where your school draws the letter-grade lines. This page covers both, plus the rounding question that decides a surprising number of B-versus-B+ arguments.
The formula
18 ÷ 30 = 0.6, and 0.6 × 100 = 60%. If you know the number you got wrong instead, subtract it from the total first: 7 wrong on a 40-question test is 33 right, and 33 ÷ 40 × 100 = 82.5%.
When every question is worth the same, each one is worth 100 ÷ (number of questions) percent. On a 30-question test that's 3.33% per question; on a 40-question test, 2.5%; on a 25-question test, 4%. That's why missing two questions hurts much more on a short quiz than on a long exam.
The letter-grade scale used here
There's no single official US grading scale, but this one is used by a large number of high schools and colleges:
| Letter | Percentage | Letter | Percentage |
|---|---|---|---|
| A | 93–100 | C | 73–76 |
| A− | 90–92 | C− | 70–72 |
| B+ | 87–89 | D+ | 67–69 |
| B | 83–86 | D | 63–66 |
| B− | 80–82 | D− | 60–62 |
| C+ | 77–79 | F | Below 60 |
Plenty of schools use a simpler 10-point scale instead (90+ is an A, 80–89 a B, and so on, with no plus or minus grades). Your syllabus or student handbook will say which one applies. The percentages in the charts don't change — only the letter next to them.
Scores out of 30
| Score | Percentage | Letter |
|---|---|---|
| 30/30 | 100% | A |
| 29/30 | 96.7% | A |
| 28/30 | 93.3% | A |
| 27/30 | 90% | A− |
| 26/30 | 86.7% | B (B+ if rounded) |
| 25/30 | 83.3% | B |
| 24/30 | 80% | B− |
| 23/30 | 76.7% | C (C+ if rounded) |
| 22/30 | 73.3% | C |
| 21/30 | 70% | C− |
| 20/30 | 66.7% | D (D+ if rounded) |
| 19/30 | 63.3% | D |
| 18/30 | 60% | D− |
| 17/30 | 56.7% | F |
| 16/30 | 53.3% | F |
| 15/30 | 50% | F |
Why 26/30 can be a B or a B+
Thirds don't divide evenly into percentages, so tests out of 15, 30 or 60 produce scores like 86.67%. Whether that's a B or a B+ depends on one decision your teacher makes: do they round before applying the cut-off?
- Unrounded, 86.67% is below the 87% line, so it's a B.
- Rounded to the nearest whole percent, it becomes 87%, so it's a B+.
On a 30-point test this happens three times: at 20/30 (D or D+), 23/30 (C or C+) and 26/30 (B or B+). A 40-question test has the same issue with half percentages — 37/40 is 92.5%, an A− as it stands but an A if it's rounded up to 93%. The same goes for 33/40, 29/40 and 25/40. Tests out of 10, 20, 25 and 50 always give whole percentages, so they never have this problem.
Scores out of 20 and 25
| Out of 20 | % | Letter | Out of 25 | % | Letter |
|---|---|---|---|---|---|
| 20 | 100% | A | 25 | 100% | A |
| 19 | 95% | A | 24 | 96% | A |
| 18 | 90% | A− | 23 | 92% | A− |
| 17 | 85% | B | 22 | 88% | B+ |
| 16 | 80% | B− | 21 | 84% | B |
| 15 | 75% | C | 20 | 80% | B− |
| 14 | 70% | C− | 19 | 76% | C |
| 13 | 65% | D | 18 | 72% | C− |
| 12 | 60% | D− | 17 | 68% | D+ |
| 11 | 55% | F | 16 | 64% | D |
| 10 | 50% | F | 15 | 60% | D− |
On a 20-question quiz each answer is worth 5%, so a single mistake moves you most of a letter grade.
Scores out of 40
| Score | % | Letter | Score | % | Letter |
|---|---|---|---|---|---|
| 40 | 100% | A | 31 | 77.5% | C+ |
| 39 | 97.5% | A | 30 | 75% | C |
| 38 | 95% | A | 29 | 72.5% | C− (C if rounded) |
| 37 | 92.5% | A− (A if rounded) | 28 | 70% | C− |
| 36 | 90% | A− | 27 | 67.5% | D+ |
| 35 | 87.5% | B+ | 26 | 65% | D |
| 34 | 85% | B | 25 | 62.5% | D− (D if rounded) |
| 33 | 82.5% | B− (B if rounded) | 24 | 60% | D− |
| 32 | 80% | B− | 23 | 57.5% | F |
Scores out of 50
Each mark on a 50-point test is exactly 2%, which makes these easy to do in your head: double the score.
| Score | % | Letter | Score | % | Letter |
|---|---|---|---|---|---|
| 50 | 100% | A | 39 | 78% | C+ |
| 48 | 96% | A | 38 | 76% | C |
| 47 | 94% | A | 37 | 74% | C |
| 46 | 92% | A− | 36 | 72% | C− |
| 45 | 90% | A− | 35 | 70% | C− |
| 44 | 88% | B+ | 34 | 68% | D+ |
| 43 | 86% | B | 33 | 66% | D |
| 42 | 84% | B | 32 | 64% | D |
| 41 | 82% | B− | 31 | 62% | D− |
| 40 | 80% | B− | 30 | 60% | D− |
Tests out of 10 work the same way, just times ten: 9/10 is 90% (A−), 8/10 is 80% (B−), 7/10 is 70% (C−) and 6/10 is 60% (D−).
Any other total
For a test out of 36, 45 or 120 points, use the formula above or let the calculator build the full chart. Enter the number of questions (or points) and it lists the percentage and letter for every possible number wrong — the same idea as the cardboard “EZ grader” slide rules teachers used to keep on their desks.
Try the free Test Grade CalculatorEnter the total and the number wrong (or points earned) to get the percentage, letter grade and a full grading chart.A test percentage isn't your course grade
One 60% on a quiz rarely sinks a course. Most classes weight categories — say homework 20%, quizzes 20%, tests 30%, final exam 30% — and a low quiz score only moves the quiz category. To see what a single score does to your overall grade, use the Weighted Grade Calculator.
And if the final is still ahead of you, our guide to what grade you need on your final shows how to work out the exact score required for the grade you want.
Frequently asked questions
What is 18 out of 30 as a percentage?
60%. Divide 18 by 30 to get 0.6, then multiply by 100. On the common US scale that's a D−, the lowest passing grade.
What is 24 out of 30 as a grade?
80%, which is a B− on the common US scale and a B on a simple 10-point scale.
Is 70% a passing grade?
Yes, at almost every US school 70% is a C−, and most schools set the pass mark at 60%. Some programmes and individual courses require 70% or higher to pass or to count toward a major, so check your course rules.
How do I work out a grade from the number of questions wrong?
Subtract the number wrong from the total to get the number right, divide by the total and multiply by 100. 5 wrong out of 25 is 20 right, and 20 ÷ 25 × 100 = 80%.
Do all schools use the same letter grades?
No. Many use the plus/minus scale on this page, others use a 10-point scale with no plus or minus, and schools outside the US use entirely different systems. The percentage is the same everywhere; only the letter changes.