How to calculate a test grade
One division and one multiplication. Take the questions you answered correctly, divide by the number of questions on the test, and multiply by 100:
That is the whole formula, and it is the same whether the units are questions, points, or marks. The interesting part is not the score — it is what the score tells you about the next test.
A worked example
These are the values loaded above.
total = 30
score = 26 ÷ 30 = 0.86666…
score = 86.67%
each question = 100 ÷ 30 = 3.33%
An 86.67% — a B+ on a plus/minus scale, a B on a straight-letter scale. You missed four, and each question was worth 3.33 percentage points.
That last number is the useful one. If you were one question away from an A- at 90%, the gap is arithmetic rather than opinion: you needed 27 correct, not 26. And it tells you whether it is worth asking about a question you think was marked unfairly — 3.33 points can cross a letter boundary, where on a 100-question test the same argument moves you 1 point and almost never changes anything.
How many can you miss?
This is the question students actually search for, and the answer depends almost entirely on test length. The number of misses you can absorb at a given target is:
Rounded down, because you cannot miss a fraction of a question. At a 90% target:
| Questions | Each worth | Misses allowed at 90% |
|---|---|---|
| 10 | 10% | 1 |
| 20 | 5% | 2 |
| 25 | 4% | 2 |
| 30 | 3.33% | 3 |
| 50 | 2% | 5 |
| 100 | 1% | 10 |
Short tests are brutal and long tests are forgiving. On a ten-question quiz a single careless mistake costs you a full letter grade; on a hundred-question final the same mistake is invisible. Worth knowing before you decide how carefully to check your work.
Points instead of questions
When questions carry different weights — a test with twenty multiple-choice items worth 2 points each and two essays worth 30 — counting questions gives you the wrong answer. Enter points instead: points earned over points possible. The formula does not change, only the units.
What this does not know
Curves. If your instructor curves, the raw score above is the input to the curve, not the final grade. Common approaches add a flat number of points, scale everyone against the top score, or fit the class to a distribution — and they produce very different outcomes from the same raw score.
Partial credit. A half-credit answer is neither right nor wrong. Convert to points before entering anything.
How much this test matters. A 60% on a quiz worth 2% of your grade is not the emergency it feels like. To find out what a test actually did to your course grade, put it into the weighted grade calculator alongside your other categories — and if you are trying to work out what you need on the final, the final grade calculator answers that directly.