Test Grade Calculator

The chart: every common quiz length

Each cell is the percentage for that many wrong answers on that length of test, computed as (total − wrong) ÷ total. Percentages are rounded half-up to one decimal place; the letters beneath them come from the exact unrounded value on a ten-point scale, because rounding before you assign a letter can push a score across a boundary it did not really cross. Blank cells mean more wrong answers than the test has questions.

What one question costs

The most useful thing in that chart is not any single cell, it is the gap between rows. On a test of N questions, each question is worth exactly 100 ÷ N percentage points:

• 5 questions — one wrong costs 20.00 points
• 10 questions — one wrong costs 10.00 points
• 12 questions — one wrong costs 8.33 points
• 15 questions — one wrong costs 6.67 points
• 20 questions — one wrong costs 5.00 points
• 25 questions — one wrong costs 4.00 points
• 50 questions — one wrong costs 2.00 points

A five-question quiz has no C grade available at all: you score 100, 80, 60, 40, 20 or 0, so the possible letters on a ten-point scale are A, B, D, F, F and F. One mistake is the difference between an A and a B; two is the difference between an A and a D. Short quizzes are enormously high-variance instruments, which is worth remembering both when you set one and when you get one back. On a 50-question test the same single mistake costs 2.00 points and almost never changes a letter.

Where the letter depends on the scale, not the score

One wrong out of twelve is 91.7%. On a ten-point scale that is an A. If your school uses a seven-point scale, where the A band starts at 93, the same paper is a B. On a plus/minus scale it is an A-minus. Same twelve questions, same one mistake, three different letters — and none of them is the "right" one outside the school that set the policy. The grade calculator's scale comparison table lists every percentage where the common scales part company.

The rounding rule matters at the same edges. Two wrong out of fifteen is 86.666…%. Taken exactly, that is a plain B on a plus/minus scale — the B+ band starts at 87 and the score is a third of a point short. Round it to 87% first and it becomes a B+. This page never rounds before assigning a letter, and states the rule next to the chart, so that if your instructor does round you can see exactly which papers it moves.

Grading a stack efficiently

1. Set the question count once. It does not change between papers in the same stack.
2. Use the minus and plus buttons for the number wrong rather than retyping — one click per paper.
3. The five-row table under the tool shows the rows either side of the current answer, so a paper one better or one worse is already on screen.
4. For a whole class, print the chart column for your test length and mark straight from it.
5. If questions are worth different amounts, stop using question counts and grade in points — the main grade calculator takes 38/45 directly.

Related calculators

• Grade calculator — put this quiz into a whole course, with categories or total points.
• Weighted grade calculator — see how much a quiz category is worth against exams.
• Final grade calculator — the score you need on the last exam of the term.