Grade Curve Calculator | Gradeculator

Grading scale

Scale

Your choice is saved for every tool on this site.

Raw scores

Scores must be 0–100. Invalid values are ignored.

Curve method

Choose how scores are adjusted.

Points to add

Added to every score (capped at 100).

Enter scores above to see curved results.

Grading scales vary by school — check your syllabus, and adjust the scale above if yours differs.

How Grade Curving Works

A grade curve adjusts raw test scores to account for an unexpectedly difficult exam or a systematic grading error. This calculator supports three standard methods used by instructors at every level.

Method 1 — Add Points

Every score is shifted up by a fixed number of points, capped at 100. This is the simplest approach and treats all students equally.

curved = min(100, raw + points)

Example: raw score of 72 with +8 points → 80 (B).

Method 2 — Scale Highest to 100

Every score is multiplied so that the highest raw score in the set becomes exactly 100. Useful when the exam was simply too hard and the top student scored, say, 88 instead of 100.

curved = min(100, (raw ÷ max) × 100)

Example: class max is 88. A raw score of 72 → (72 ÷ 88) × 100 = 81.8 (B).

Method 3 — Square-Root Curve

Takes the square root of each raw score and multiplies by 10. This compresses the scale at the top while giving the biggest boost to low scores — the most redistributive option.

curved = min(100, √raw × 10)

Example: raw score of 64 → √64 × 10 = 80 (B). A raw score of 100 stays at 100 (A).

Method 4 — Bell Curve (Normal-Distribution Rescale)

Fits the class scores to a normal distribution and shifts the mean to your chosen target while optionally adjusting the spread. Every student's relative position within the class (their z-score) is preserved exactly.

z = (raw − class mean) ÷ class SD

curved = clamp(targetMean + z × targetSD, 0, 100)

When Target SD is left blank the original spread is kept, so only the mean shifts. Example: class scores 60, 70, 80, 90 (mean = 75). Setting target mean to 80 shifts every score up by 5: 65, 75, 85, 95. The top student is no longer capped at a fixed maximum — the rescale is symmetrical around the new mean.

Worked Example

Suppose a class of 5 students scored: 55, 63, 72, 81, 88. Applying a scale-to-100 curve (max = 88):

55 → 62.5% (D) | 63 → 71.6% (C)

72 → 81.8% (B) | 81 → 92.0% (A)

88 → 100.0% (A)

The class average rises from 71.8% to 81.6% — a full letter grade improvement with no student's relative ranking changing.

Also see: Test Grade Calculator to score individual tests, and Semester Grade Calculator to combine weighted categories into an overall course grade.

Frequently Asked Questions

What is a grade curve and why do teachers use it?

A grade curve adjusts raw test scores upward so that the class distribution better reflects expected performance. Teachers curve grades when a test is unexpectedly difficult, when the class average falls well below the desired target, or when a mistake in the test makes certain questions unfairly hard. Curving does not mean everyone gets an A — it means each score is shifted by a consistent method.

What is the difference between adding points, scaling to 100, and a square-root curve?

Adding points shifts every score up by a fixed amount (e.g. +5 points means a 72 becomes a 77). Scaling to 100 multiplies every score so the highest raw score becomes 100 — useful when the test was simply too hard and the best student only scored an 88. The square-root curve takes the square root of each score and multiplies by 10, which helps low scores more than high scores (e.g. a 64 becomes 80, but a 100 stays 100).

Which curve method is fairest for students?

It depends on the situation. Adding points is the simplest and treats all students equally. Scaling to 100 rewards the top performer and proportionally helps everyone else. The square-root curve gives the biggest boost to the lowest scorers, making it the most redistributive option. Many instructors prefer scaling to 100 because it anchors the curve to actual student performance rather than an arbitrary point value.

Can a curved score exceed 100%?

This calculator caps all curved scores at 100%. In practice, some instructors allow scores above 100% as extra credit — if you need that, take the raw curved value before the cap and add it to your gradebook manually.

How does the scale-to-100 method work when the top score is already 100?

If the highest score in your set is already 100, scaling to 100 does nothing — every score is multiplied by 100/100 = 1. This is the expected behaviour: if someone already earned a perfect score, there is no headroom to scale into.

What is a bell-curve grade adjustment and how does the calculator apply it?

A bell-curve adjustment (also called a normal-distribution rescale) repositions the entire class distribution so it centres on a target mean while preserving every student's relative standing. The calculator computes each score's z-score — how many standard deviations it sits above or below the class average — then places that z-score the same distance from your chosen target mean. For example, if the class mean is 68% and you set a target mean of 75%, every score shifts up by 7 percentage points without changing anyone's rank. Optionally you can also set a target standard deviation to widen or narrow the spread; leaving it blank keeps the original spread intact. All results are clamped to 0–100.