How to read these tables
Each row is one possible outcome. Find the number you got right in the left column and read across for the percentage and the letter. The Missed column is there because it is usually the number you actually remember walking out of the room — you know you missed four, not that you scored 86.67%.
Letters use the plus/minus scale, where an A starts at 93, a B at 83 and a C at 73. If your school uses straight letters instead — A at 90, B at 80, C at 70 — the percentages are identical and only the letter column shifts. Both scales are laid out side by side on the grade conversion chart.
Why short tests hit harder
One question is worth 100 ÷ total percentage points, and that number changes the stakes enormously:
| Test length | One question | One mistake takes 100% down to |
|---|---|---|
| 10 | 10 pts | 90% — A- |
| 15 | 6.67 pts | 93.33% — A |
| 20 | 5 pts | 95% — A |
| 25 | 4 pts | 96% — A |
| 30 | 3.33 pts | 96.67% — A |
| 50 | 2 pts | 98% — A |
On a ten-question quiz a single careless error costs you a full letter grade. On a fifty-question exam the same error is invisible. That asymmetry is worth remembering when you are deciding how carefully to check your work — and when you are deciding whether a marked-wrong answer is worth querying with your instructor. On a short quiz it genuinely can change your letter; on a long exam it almost never does.
A worked example
Take 22 out of 25, the kind of score that sits right on a boundary.
missed = 3
each question = 100 ÷ 25 = 4%
88% → B+ on plus/minus (B+ runs 87–89.99)
88% → B on straight letter (B runs 80–89.99)
One more correct answer would have been 92% and an A-. One fewer would have been 84% and a plain B. Three questions cover two letter grades on a 25-question test, which is exactly why the boundary rows in these tables are the ones worth knowing before you hand the paper in.
Points instead of questions
When questions carry different weights, count points. A 50-point test where you earned 43 is 86%, regardless of whether that was one big miss or several small ones — read the "out of 50" table with points in place of question counts and it works identically.
For a test length not listed here, the test grade calculator takes any number and also shows how many you can afford to miss to hold a target. To find out what a given test did to your overall course grade, put it into the weighted grade calculator — a 78% on a quiz worth 5% of the course is not the emergency it feels like.