How Test Grades Are Calculated
A test grade is a percentage that represents how many questions, points, or problems you answered correctly out of the total available. The calculation is straightforward: divide the number of correct responses by the total number of questions, then multiply by 100 to convert to a percentage. This percentage is then mapped to a letter grade using a grading scale.
Most standardized tests, classroom quizzes, and exams use this simple percentage-based scoring. Each question is typically worth the same number of points (equal weighting). Some tests assign different point values to different questions. In that case, divide your total earned points by total possible points instead of counting questions.
The Test Grade Formula
Test Grade (%) = (Number Correct / Total Questions) x 100
Equivalently, if you know the number wrong:
Test Grade (%) = ((Total Questions - Number Wrong) / Total Questions) x 100
Both formulas produce the same result. Use whichever matches the information you have.
Maya took a 40-question biology exam and got 6 wrong. Her score: (40 - 6) / 40 x 100 = 34 / 40 x 100 = 85.0% (B). If each question were worth 2.5 points (total 100 points), Maya earned 85 out of 100 points, giving the same 85% result.
Standard Grading Scale
The standard American grading scale maps percentage scores to letter grades. Most schools use either the "standard" scale (with 7-point ranges) or the simpler "10-point" scale.
| Letter Grade | Percentage Range | GPA Points | Description |
|---|---|---|---|
| A+ | 97-100% | 4.0 | Exceptional |
| A | 93-96% | 4.0 | Excellent |
| A- | 90-92% | 3.7 | Excellent |
| B+ | 87-89% | 3.3 | Very Good |
| B | 83-86% | 3.0 | Good |
| B- | 80-82% | 2.7 | Good |
| C+ | 77-79% | 2.3 | Above Average |
| C | 73-76% | 2.0 | Satisfactory |
| C- | 70-72% | 1.7 | Below Average |
| D+ | 67-69% | 1.3 | Poor |
| D | 63-66% | 1.0 | Poor |
| D- | 60-62% | 0.7 | Barely Passing |
| F | 0-59% | 0.0 | Failing |
Source: Standard U.S. grading scale. Exact ranges vary by institution and instructor.
How Many Can I Miss?
The number of questions you can miss and still achieve a given grade depends on the total questions on the test. The table below shows the maximum wrong answers allowed for common test lengths.
| Total Questions | Max Wrong for A (90%) | Max Wrong for B (80%) | Max Wrong for C (70%) | Max Wrong for D (60%) |
|---|---|---|---|---|
| 10 | 1 | 2 | 3 | 4 |
| 20 | 2 | 4 | 6 | 8 |
| 25 | 2 | 5 | 7 | 10 |
| 30 | 3 | 6 | 9 | 12 |
| 40 | 4 | 8 | 12 | 16 |
| 50 | 5 | 10 | 15 | 20 |
| 75 | 7 | 15 | 22 | 30 |
| 100 | 10 | 20 | 30 | 40 |
Based on standard grading scale where A = 90%+, B = 80%+, C = 70%+, D = 60%+. Individual instructor scales may vary.
On shorter tests, every question is high-stakes. A 10-question quiz leaves almost no room for error: missing just 2 drops you to 80% (B-). On a 100-question exam, you can miss 10 and still earn an A-. This is why Tom, who tutors students at Pinewood Falls, tells them to slow down on short quizzes: "On a 10-question quiz, each answer is worth as much as 10 answers on a 100-question final."
Understanding Curved Grades
Some instructors curve test grades when class performance is lower than expected. Common curving methods include: adding a flat number of points to every score, scaling so the highest score in the class becomes 100%, or adjusting the grading scale so the class average maps to a B or C.
For example, if the class average is 65% and the instructor curves to a 78% average, every student receives +13 points. A raw 72% becomes 85% (B). A raw 58% becomes 71% (C-). Curved grading does not change the underlying test score calculation, but it shifts the scale that determines your letter grade.
To use this calculator with a curved test, either enter the adjusted total points (if points were added) or compare your raw percentage to the curved grading scale your instructor provides. You can then use the grade calculator to see how this test score affects your overall course grade, the GPA calculator to project how the course grade impacts your semester GPA, or the percentage calculator for quick score-to-percentage conversions.
This calculator provides estimates for educational purposes only. Grading scales and policies vary by institution and instructor. Consult your syllabus for your specific course grading criteria.