How to Calculate a Grade Percentage
One assignment, one division
Every points-to-percent conversion is the same operation. 43 out of 50: 43 ÷ 50 = 0.86 → 86%. 117 out of 140: 117 ÷ 140 = 0.836 → 83.6%. If decimals trip you up, a shortcut for clean denominators: out of 50, double both numbers (86/100); out of 25, multiply by 4; out of 20, multiply by 5. For anything else, the division is what calculators are for.
The pitfall: you can't just average percentages
Here's where most hand calculations go wrong. Suppose your course has two graded items so far: a quiz scored 8/10 (80%) and an exam scored 90/100 (90%). The tempting move is (80 + 90) ÷ 2 = 85%. The true grade is total earned over total possible: (8 + 90) ÷ (10 + 100) = 98 ÷ 110 = 89.1%.
| Item | Earned | Possible | Percent |
|---|---|---|---|
| Quiz | 8 | 10 | 80% |
| Exam | 90 | 100 | 90% |
| Naive average | — | — | 85% ✗ |
| True grade | 98 | 110 | 89.1% ✓ |
Why the 4-point gap? The exam is worth ten times the quiz's points, so it should pull ten times as hard — averaging the percentages pretends they're equals. The naive average only matches the true grade when every item is worth identical points. In a points-based course, the point values are the weights.
Whole-course percentage, step by step
List every graded item, sum the earned column, sum the possible column, divide once. Example: quizzes 47/60, homework 138/150, midterm 82/100, project 88/90. Totals: 355 earned, 400 possible → 355 ÷ 400 = 88.75%. Two checks before trusting the number: exclude anything not yet graded (don't count it as 0/possible), and apply any dropped-lowest policy from the syllabus before summing. If your course uses weighted categories instead of raw points, this method doesn't apply — you need the weighted-average formula instead.
Try it yourself: Percentage Calculator
Type earned and possible points — the percentage and letter grade appear instantly.
Frequently asked questions
How do I turn a percentage back into points?
Multiply the percentage (as a decimal) by points possible. Needing 90% on a 140-point exam means 0.90 × 140 = 126 points. Useful in reverse when planning what a target grade requires.
Is 86% the same grade everywhere?
The percentage is universal; the letter isn't. On the common U.S. scale 86% is a B, but some schools draw B+/B or 10-point-scale lines differently. Percentages travel; letters are local.
When is averaging percentages actually correct?
Only when every item carries equal weight — either identical point values, or a syllabus that explicitly says each counts equally (e.g., "four exams, 25% each"). Then the average of the percentages and the points method agree exactly.