Grade Curve Calculator
The test was harder than you planned — now what? Paste your class scores into this grade curve calculator, pick a curve, and see every student's grade before and after, plus the new class average. Built for teachers; students can use it to see how a curve would change their grade.
class average before → after the curve · 8 scores · highest raw score 95%
| # | Original | Letter | Curved | New letter | Change |
|---|---|---|---|---|---|
| 1 | 58% | F | 61.1% | D- | +3.1 pts |
| 2 | 64% | D | 67.4% | D+ | +3.4 pts |
| 3 | 71% | C- | 74.7% | C | +3.7 pts |
| 4 | 72% | C- | 75.8% | C | +3.8 pts |
| 5 | 78% | C+ | 82.1% | B- | +4.1 pts |
| 6 | 83% | B | 87.4% | B+ | +4.4 pts |
| 7 | 89% | B+ | 93.7% | A | +4.7 pts |
| 8 | 95% | A | 100.0% | A+ | +5.0 pts |
Curved scores are capped at 100%.
The three curve methods, explained
1. Add flat points
The simplest curve: every score rises by the same amount. A class with a 71% average on a brutal exam might get +7 across the board. It preserves the gaps between students exactly and is easy to explain — its weakness is that it also rewards the top scores, which are usually capped back at 100.
2. Scale to the highest score
The best raw score becomes 100%, and every other score is stretched by the same ratio: curved = score ÷ highest × 100. If the top student scored 92, everyone's grade rises by about 8.7% of its value. Rankings and relative gaps stay intact.
3. Square root curve
Curved = 10 × √score. This one deliberately helps the bottom most: 36 → 60, 49 → 70, 64 → 80, while 90 → 94.9 and 100 → 100. It is the most generous curve for struggling students and the least distorting at the top — which is why it is a favourite for very hard exams.
After curving, students checking their standing can run their new percentage through the grade calculator to see what it does to their course grade, or convert it to a letter with the grade percentage calculator.
Frequently asked questions
How does a grade curve work?
A grade curve adjusts a set of scores upward to correct for a test that was harder than intended. Common methods: add the same points to everyone (flat), rescale so the highest score becomes 100% (linear scale), or take the square root of each score times 10, which lifts low scores the most. This calculator applies all three and shows the class average before and after.
What is the square root curve formula?
Curved score = 10 × √(raw score). A 64 becomes 80, a 49 becomes 70, and an 81 becomes 90. It helps struggling students the most while barely moving top scores (a 100 stays 100).
How does scaling to the highest score work?
Every score is divided by the highest score in the class and multiplied by 100. If the top score was 92, a raw 92 becomes 100, and a 70 becomes 70 ÷ 92 × 100 = 76.1. The whole distribution stretches by the same ratio, so the ranking never changes.
Is curving grades fair?
It depends on why you curve. Curving compensates for a genuinely harder-than-planned exam, which most teachers and students consider fair. Curving to a fixed distribution (forcing a set number of A's and F's) is more controversial. Flat and square-root curves only ever raise grades, which is why they are the most common in practice.
Can a curve ever lower a grade?
Not with the three methods in this calculator — flat points, scale-to-highest and square root curves only raise scores (or leave a 100 at 100). Nothing here ever reduces a student's grade.
How do I convert curved percentages back to letter grades?
The results table already shows the new letter grade for every score on the standard scale (93%+ = A, 90–92% = A-, 87–89% = B+, and so on). For a single score, the grade percentage calculator does the same conversion.