How to use the grade curve calculator
Paste your class's raw scores into the Grades box — separated by commas, spaces, or one per line — or click Import CSV to pull numbers straight from a spreadsheet export. Set the highest possible grade (100 by default), pick a curve method, and your curved results appear instantly: a before/after letter-grade bar, class-wide statistics, and every student's new score.
The default methods cover the three most common curves. Tap Go advanced for bell curve, square root, target-mean, and multiply-by-factor methods.
Curve methods explained
Add points (flat): adds the same number of points to every score. The simplest and most common curve — it never changes the ranking between students.
Highest grade → 100%: multiplies every score by whatever factor brings the top score in your list up to your highest possible grade.
Percentage boost: increases every score by a fixed percentage of itself, so higher scores gain more raw points than lower ones.
Reach a target mean: adds or subtracts a fixed number of points so the class average lands exactly on the mean you choose.
Bell curve: converts every score to a z-score against the original mean and standard deviation, then maps it onto a new mean and standard deviation you set.
Square root: takes the square root of each score (as a fraction of the max) and rescales it — this boosts low scores far more than high ones.
Multiply by factor: multiplies every score by a fixed number you choose.
Worked example
Ten raw scores: 80, 80, 75, 60, 60, 55, 50, 50, 40, 25 (out of 100). The class average is 57.5%.
A flat +10 curve brings every score up by 10 points, so 25 becomes 35 and 80 becomes 90 — the gaps between students stay exactly the same. A bell curve targeting a mean of 75 with a standard deviation of 12 would instead reshape the whole spread: the same 80 becomes about 91, but a 55 becomes about 73 — a bigger jump for scores near the original average.
Which method should I use?
Use Add points or Highest → 100% when a test was simply harder than expected and you want to preserve everyone's exact ranking. Use Square root when you want to help struggling students more than top performers. Reach for Bell curve only when you need to standardize results across multiple sections or match an institutional grading policy — it's the one method that can lower an above-average score.
Related tools
Need to know what score you need on an upcoming exam instead? Try the Final Grade Calculator. Averaging category weights like homework, quizzes and a final? The Weighted Average Calculator uses the same underlying math as this tool's weighted methods.
Common questions
What is the easiest way to curve grades?
Add a fixed number of points to every student's score — usually enough to bring the highest score up to 100%. It's the simplest method because it shifts every grade by the same amount, so the ranking between students never changes.
How does a bell curve grading work?
A bell curve recalculates every score using z-scores: it finds how many standard deviations each raw score is from the class average, then maps that same distance onto a new target mean and standard deviation that you choose. This can raise some grades and lower others, since it forces the whole class onto a normal distribution instead of just shifting everyone up.
How does the square root curve work?
Take the square root of each score (as a fraction of the highest possible grade) and scale it back up. Because square roots compress large numbers less than small ones, this boosts low scores a lot more than high scores — a 50% can jump to roughly 71%, while a 90% only rises to about 95%.
Can a curve lower a grade?
Flat-point, percentage-boost, square-root, and highest-to-100% curves only ever raise or hold scores steady. A bell curve is the exception — because it forces a specific target mean and spread, students well above the original average can end up with a lower curved score than their raw one.
What is a normal grade curve distribution?
A commonly cited version assigns roughly the top 10-15% of a class an A, the next 20-25% a B, the middle 40-50% a C, the next 10-15% a D, and the bottom 5-10% an F — following a standard bell-shaped (normal) distribution. This calculator's letter-grade bar uses the more common straight 90/80/70/60 percentage bands so you can compare before and after on the same scale.