How 18 out of 30 works out to 60%
Divide the score by the total and multiply by a hundred: 18 ÷ 30 × 100 = 60%. Each of the 30 questions is worth 3.33%, so the grade can only land on multiples of 3.33% — there is no way to score 61.7% on a thirty-question test.
In lowest terms 18 out of 30 is 3 out of 5 — the same fraction with 6 divided out of both halves. That is worth noticing when a score looks unfamiliar: 3 out of 5 is the shape most people can read at a glance.
12 questions were wrong out of 30, and together they cost 40%. If any of them were marked with partial credit the real figure is a little higher — the test grade calculator takes half marks.
60% as a letter grade
Schools do not all cut letters at the same percentage, so 60% has more than one correct answer. Here is where it lands on the three scales in common US use:
| Scale | Where 60% lands | Grade points |
|---|---|---|
| Plus/minus, the most common US scale | D- | 0.70 |
| Straight letters, 90/80/70/60 | D | 1.00 |
| Seven-point, 93/85/77/70 | F | 0.00 |
On the plus/minus scale this site uses throughout, 18 out of 30 is a D-, worth 0.70 grade points on an unweighted 4.0 scale. A school that grades in straight letters, with no pluses or minuses, would record the same score as a D. On a seven-point scale, where the bands are seven points wide instead of ten, it drops to an F — the same work, a different transcript. The full band table for all three, and what each letter is worth on the 4.0, 4.3 and 5.0 scales, is on letter grade to GPA.
If this grade came from a weighted class the grade points move rather than the letter: 0.70 becomes 1.20 in an honors class and 1.70 in an AP or IB class, on the usual +0.5 and +1.0 bumps. The high school GPA calculator applies those automatically.
What it takes to reach a D
The next letter up is a D, which starts at 63%. On a thirty-question test that is 19 out of 30 — one more correct answer than you have. Going the other way, 18 out of 30 is the lowest score that still counts as a D- — you are exactly on the boundary, and one more wrong answer would have made it an F.
The scores either side of 18 out of 30
One more correct answer is 19 out of 30, 63.3% — a D. One fewer is 17 out of 30, 56.7% — an F. Nothing exists in between. A thirty-question test has exactly 30 achievable grades above zero and 60% is one of them; a percentage that is not a multiple of 3.33% cannot come off a test this length, whatever a rounding rule does to it afterwards.
What 60% does to a course average
One test is rarely the whole grade. If everything else in the course is averaging 85% and this test is worth the share in the left-hand column, the course grade lands here:
| Test is worth | Course grade | Letter |
|---|---|---|
| 10% of the course | 82.5% | B- |
| 20% of the course | 80% | B- |
| 30% of the course | 77.5% | C+ |
| 40% of the course | 75% | C |
Because 60% is below that 85% baseline, this test pulls the course average down by 5 points at a 20% weighting. Weightings vary, and a syllabus that puts the final at 30% is a different problem from one that puts it at 10% — put your own categories into the grade calculator, or work backwards from the grade you need with the final grade calculator.
60% on other test lengths
60% is not unique to a thirty-question test. The same percentage comes out of 6 out of 10, 12 out of 20, 15 out of 25, 24 out of 40, 30 out of 50, 36 out of 60 and 60 out of 100. The letter grade is identical on all of them, because the letter only ever looks at the percentage. What differs is the granularity: 18 out of 30 moves in steps of 3.33%, while 60 out of 100 moves in steps of 1%, so the longer test can express grades the shorter one simply cannot reach.
About thirty-question tests
A thirty-question test, a typical end-of-unit or end-of-chapter paper. Every score on one, from 1 to 30, is charted on the out of 30 page, and the easy grader turns the same table around for marking a stack of papers: count what is wrong rather than what is right.