Grade Curve Calculator
Free grade curve calculator: paste a column of scores and curve them by a flat bump, top-score-to-100, a target average, or a bell curve. See every before/after grade and download the curved column as CSV.
| Original | Curved | Δ |
|---|---|---|
| 55 | 60 | 5 |
| 61 | 66 | 5 |
| 64 | 69 | 5 |
| 68 | 73 | 5 |
| 72 | 77 | 5 |
| 75 | 80 | 5 |
| 78 | 83 | 5 |
| 83 | 88 | 5 |
| 88 | 93 | 5 |
| 91 | 96 | 5 |
What curving grades means
Curving grades means applying the same rule to every score to shift the whole set — usually upward — without re-grading anyone individually. Teachers curve for many reasons: a test ran harder than intended, a question was flawed, or a department targets a particular class average. This calculator offers four common methods and shows you exactly what each does to every student before you commit to one.
The four methods
The four methods: a flat bump adds the same number of points to everyone (the simplest curve). Top-score-to-100 finds the highest score and adds that gap to 100 to every grade, so the best paper becomes 100 and everyone rises equally. Scale-to-target-average shifts the whole set so the class mean lands on a number you choose, keeping the spread between students the same. A bell curve re-stretches the scores to a target mean and standard deviation, which changes the spread as well as the center. Optionally cap any method at 100.
Worked example
Take five scores: 55, 65, 75, 85, 95 (average 75). A flat bump of +5 makes them 60, 70, 80, 90, 100 and moves the average to 80. Top-score-to-100 adds 100 − 95 = 5 — here the same result. Scaling to a target average of 85 shifts every score up by 10 (85 − 75), giving 65, 75, 85, 95, 105 (cap at 100 if you do not allow scores above 100). A bell curve to mean 85, SD 10 re-spaces them around 85 based on how far each sat from the original average.
Curving is a policy choice
Curving is a policy choice, not a statistical requirement — nothing about a set of scores says it must be curved, and different methods reward different students. A flat bump helps everyone equally; top-score-to-100 helps most when the best score is well short of 100; scaling to an average changes the center without touching the spread; a bell curve can pull in a wide spread or push out a narrow one. Look at the before/after table for each method before deciding, and be transparent with students about which rule you used.
How to use it
- Paste your scores into the box — one per line, straight from your gradebook.
- Choose a curve method and enter its setting (points to add, target average, or target mean and SD).
- Review the before/after table and the chart; switch the chart view to compare distributions.
- Download the curved column as CSV to paste back into your gradebook, or save the chart as PNG, SVG, or PDF.
FAQ
- How do I curve grades to a certain average?
- Paste your scores, choose the "Scale to target average" method, and enter the average you want (for example 75). The calculator shifts every score by the same amount so the class mean lands on your target, and shows the new grade for each student.
- What is a bell curve grading scale?
- Bell-curve grading re-fits scores to a normal distribution with a chosen mean and standard deviation, so grades spread out around the target center. It changes the spacing between students, not just the average. Use the "Bell curve" method here and set the target mean and SD.
- Can I stop curved scores from going over 100?
- Yes — turn on "Cap at 100" and any curved score above 100 is clamped to 100. Leave it off if your policy allows extra-credit-style scores above 100.