Curve a class list in seconds
This curve grades calculator takes a whole class list and applies the curving methods teachers actually use: a bell curve that re-centres the class on a target mean and spread, a flat curve that adds the same points to everyone, highest score to 100, a linear scale between a new lowest and highest score, and the square-root curve. It shows each student’s raw percentage, z-score, curved score, change and letter grade, plus the class mean, median and standard deviation before and after.
It also writes the matching Excel or Google Sheets formula, so you can curve grades in Excel yourself, and exports the curved list as CSV. Students checking their own course grade should use the grade calculator instead.
How to use the Curve Grades Calculator
- Paste the class scores, one student per line (“Asha, 72”), or just the numbers separated by spaces.
- Set what the test was marked out of; every score is turned into a percentage first.
- Choose a curve method and fill in its settings — target mean and SD, points to add, or the new lowest and highest.
- Decide whether to cap scores at 100% and whether a curve may ever lower a score.
- Read the table, compare the two histograms, then copy the table, download the CSV or reuse the Excel formula.
Curve Grades Calculator features
Five curving methods
Bell curve, flat points, highest-to-100, linear range scaling and square root, switched with one menu.
z-scores for every student
Each raw score’s distance from the class mean in standard deviations.
Before and after statistics
Mean, median, SD, lowest, highest and the number of students above an F.
Three letter scales
A 90 / B 80 / C 70 / D 60, plus/minus, or relative letters from z-score bands.
Spreadsheet formula
The exact formula for the method and settings you chose.
Curving grades formulas
All formulas work on percentages, p = score ÷ out of × 100, and results never go below 0.
| Method | Formula | Effect |
|---|---|---|
| Flat curve | p + k (k = 100 − highest if blank) | Everyone gains the same points; spread unchanged |
| Highest to 100 | p × 100 ÷ highest | Proportional: higher scores gain more |
| Linear scale | L + (p − min) ÷ (max − min) × (H − L) | Lowest becomes L, highest becomes H |
| Square root | 10 × √p | Low scores gain most; 100 stays 100 |
| Bell curve | μ′ + (p − μ) ÷ σ × σ′ | New mean μ′ and SD σ′; ranks unchanged |
How the bell curve calculator for grades works
A bell curve first standardises each score: z = (p − μ) ÷ σ, where μ is the class mean and σ the standard deviation (population SD, Excel’s STDEV.P). The curved score is μ′ + z × σ′. With the example class (mean 69.83, SD 12.16) and a target of 75 with an SD of 10, Diego’s 91 has z = +1.74 and becomes 92.4; Hiro’s 48 has z = −1.80 and becomes 57.0. The new class mean is exactly 75.
Because it rescales the spread as well as the centre, a bell curve can lower the top scores of a strong class. Tick “Never lower a student’s score” to keep each student at the higher of the raw and curved score. Bell-curve grading in the strict sense assigns letters by position rather than by points; choose “Relative, by z-score bands” for A at z ≥ 1.5, B from 0.5, C from −0.5, D from −1.5 and F below. On a normal distribution that gives roughly 7% A, 24% B, 38% C, 24% D and 7% F.
Curve grades in Excel
Put the percentages in column B starting at B2 and copy the formula shown under the table down the column. For a class of 12 the bell curve is =MIN(100,MAX(0,75+STANDARDIZE(B2,AVERAGE($B$2:$B$13),STDEV.P($B$2:$B$13))*10)); the square-root curve is =10*SQRT(B2). Use STDEV.S only if your school treats the class as a sample — the results differ slightly in small classes.
Choosing a curve
- A test that was simply too hard: a flat curve or highest-to-100 keeps the order and the gaps fair.
- Very low scores: the square-root curve lifts a 36 to 60 and a 64 to 80 but moves a 96 only to 98.
- Comparing sections marked by different teachers: a bell curve puts both on the same mean and spread.
- Small classes (under about 20) rarely look normal, so z-score letter bands can be harsh. Check the histogram before using them.
Curve Grades Calculator FAQ
How do you curve grades?
Turn each score into a percentage, then apply one rule to everyone: add the same points (flat), multiply so the top score is 100, map the range linearly, take 10 × the square root, or re-centre on a target mean and SD (bell curve). This curve grades calculator does each one and shows the change for every student.
What is the formula for a bell curve on grades?
New score = target mean + (score − class mean) ÷ class SD × target SD. With a target of 75 and SD 10, a score one SD above the mean becomes 85.
How does the square-root curve work?
New score = 10 × √(percentage). 49% becomes 70% and 81% becomes 90%. Low scores gain the most and 100 stays 100.
Can curving lower a grade?
A bell curve or linear scale can, when the class mean is already above the target or the top score is mapped down. Flat, highest-to-100 and square-root curves never lower a score. Tick “Never lower a student’s score” to prevent it.
Should I use population or sample standard deviation?
For describing one class, the population SD (STDEV.P) is standard and is what this calculator uses.
Are the names I paste stored?
No. The list stays in your browser tab and nothing is uploaded.