How to curve grades
- Paste your scores, one per line. A name before each score is kept, so you can paste two columns straight from a spreadsheet.
- Choose a Curve and set it: points to add, what the top score becomes (Scale), or the target mean and standard deviation. Set Points possible if the test isn’t out of 100.
- Copy or download the curved scores. They come out in the same order, tab-separated, so they paste back into a spreadsheet column. The line under the box compares the average, middle, highest and lowest score before and after.
The four curves compared
The sample class (78, 85, 62, 91, 55, 70, 66, 88) under each method, out of 100:
| Score | Add 5 | Scale top to 100 | Square root | Bell (mean 75, SD 10) |
|---|---|---|---|---|
| 91 | 96 | 100 | 95 | 89 |
| 85 | 90 | 93 | 92 | 84 |
| 78 | 83 | 86 | 88 | 78 |
| 55 | 60 | 60 | 74 | 59 |
Adding points and scaling keep the gaps between students much as they were. The square root curve compresses them, helping the lowest scores most. The bell curve sets the class average and spread directly, whatever the test’s difficulty.
Choosing a curve
If a test was simply harder than intended, adding the same points to everyone, or the gap between the top score and full marks, is the easiest to explain to students. Scaling suits tests where nobody came close to full marks. A square root curve is a quick fix for a test where many students struggled. Bell curves are common in large courses that aim for a set grade distribution. To work out a single student’s grade from points, use the grade calculator.