Test Score Calculator
Enter how many questions you answered correctly and how many there were, and get the score as a percentage, the letter grade and the error rate — plus a z-score and percentile when you know how the class did.
The percentile assumes class scores follow a normal curve — it estimates the share of classmates you outscored, not your exact class rank.
Formula and calculation
Worked example
For 42 correct out of 50 on the plus/minus scale: the score is 84%, a B, with 8 questions missed — an error rate of 16%. If the class averaged 70% with a standard deviation of 10, the z-score is 1.4 and the estimated percentile is 91.92%.
What the results mean
- Score
- Your score as a percentage: correct answers divided by the total, times 100. This is the number a gradebook records, and the one the letter grade is based on.
- Letter grade
- The letter your percentage falls in on the selected scale. Cutoffs differ between schools, so treat a score sitting right on a boundary as uncertain.
- Questions missed
- How many questions you missed — the total minus the correct answers. This is the list to work through when you review the test.
- Error rate
- The share of the test you got wrong, as a percentage. An error rate of 20% means one question in five was missed.
- Z-score
- How many standard deviations your score sits from the class average. Zero is exactly average; above 2 is roughly the top of a normal curve. Shown when you enter both the class average and its standard deviation.
- Estimated percentile
- The estimated share of the class you outscored, assuming class scores follow a normal curve — a z-score of 0 is the 50th percentile. Treat it as an estimate of standing, not your exact rank.
Frequently asked questions
How do I calculate my test score percentage?
Divide the number of correct answers by the total number of questions and multiply by 100: 42 out of 50 is 42 ÷ 50 × 100 = 84%. The letter grade, error rate and z-score all follow from that percentage.
What is a z-score on a test?
It measures how far your score is from the class average, in units of the class standard deviation: z = (your score − class average) ÷ standard deviation. A z of 0 is exactly average, and a z of 1.5 means you scored one and a half spreads above the class.
Is the percentile the same as my class rank?
No. The percentile assumes scores follow a normal curve and estimates the share of classmates you outscored. A rank is a count of actual people, and real class distributions are lumpier than the curve — often with a clump of high scores that lowers your percentile.
What letter grade is 80%?
On the simple 90/80/70/60 scale, 80% is a B. On the plus/minus scale it is a B−, because a plain B starts at 83. Use whichever scale your syllabus prints — the page shows the full table for both.
Can I use this for a test with partial credit?
Yes, as long as both numbers are in the same units. Enter the points you earned and the points the test was worth — 34.5 out of 40 produces the same percentage as counting questions, 86.25%.