Grade Curve Calculator

How this is calculated

Every other tool on this site reads its deciding input off a document you already have — a syllabus, a transcript, a policy your registrar published. This one can't, and saying so is the page. A curve method is the instructor's private choice, is almost never written down, and moves the answer by more than a letter grade. So this page computes all four documented methods and refuses to pick one.

The fourth is the one with a citation behind it. Mehvar (2025) writes it exactly that way — “Adjusted Score = Adjusted Mean + (Adjusted SD/Raw SD) × (Raw Score − Raw Mean)” — and points out that holding the SD ratio at 1 collapses it into shifting every score by a constant, which is the first method on the list.

The worked example this page loads with

A raw 68% — a D+ on the plus/minus cut-offs — in a class that averaged 66 with a spread of 12, whose top score was 88, where the instructor either added 7 points or aimed for a 77 average with a spread of 10:

Three different letters from one piece of work, spanning 7.5 percentage points, and every one of them is a defensible application of a documented method. Nothing about the score you were handed tells you which row you're on.

Three of the four are the same operation

This is the finding that shapes the page. Write each method as a straight line — curved = intercept + slope × raw — and three of them are that line with one constant pinned:

• Flat addition is the line with the slope held at 1. Everyone moves the same distance, so the gaps between students are untouched.
• Scaling to the top score is the line with the intercept held at 0. Everyone is multiplied by the same ratio, so the student who was already ahead gains the most points — a 100 ÷ 88 stretch is worth 12 points at the top of the class and 6 at the bottom.
• Fitting a mean and a spread is the line with both free. It is the general case, and the other two are it with a knob taped down.
• The square-root curve is not a line at all, which is why it is the only one that changes the shape of the class rather than sliding or stretching it. It is also the only one with no institutional publisher: no university calendar or registrar defines it, and it circulates purely as classroom practice.

What the square-root curve actually does

It is usually described as helping the weakest students most. That is wrong at the bottom, and the arithmetic says so plainly. The gain is 10√raw − raw, which peaks at a raw 25% — worth 25 points, turning a 25 into a 50 — and falls away on both sides of it. A raw 0 gains exactly nothing, because the square root of zero is zero. A raw 100 gains nothing either: the top is a fixed point, and no score is ever pushed above it. What the curve really favours is the lower middle of the class, not its floor.

A curve can take points away

Only one of the four can, and it is the one institutions actually mandate. Fitting the class to a target spread narrower than its real one pulls the top down: a 90 in a class fitted to a 77 average with a spread of 4 comes back an 85. Michigan State's College of Law publishes precisely this as a requirement — a target mean of 3.00 in first-year classes, 3.33 in upper-level ones, tolerances of ±0.07 to ±0.17 depending on class size, and no more than 70% of any class in the B range. In a section that did unusually well, that curve is a subtraction. “Curved” is not a synonym for “raised”.

What it assumes

• Every score is a percentage out of 100. If your instructor added 5 points to a 60-point test, that is 8.3 percentage points, not 5 — convert before typing it in. The Test Grade Calculator turns marks into a percentage first.
• Nothing is capped. A flat addition can carry a score past 100 and this page will say so, because whether your instructor clipped it at 100 is another undocumented choice. Scaling to the top score puts exactly one person at 100 by construction.
• The spread is a standard deviation. If your instructor announced a “spread” or a range instead, it is not the same number and the fit will be wrong. A class of identical scores has no spread to stretch, so that method returns no answer rather than dividing by zero.
• A curve never reorders the class. All four methods are increasing, so whoever was ahead of you before is ahead of you after. What changes is how far ahead — and under the three linear methods, not even that: the ratio of the gaps survives untouched.
• One assessment at a time. This curves a single score. Feeding the curved figure into a course grade is the Weighted Grade Calculator's job.

Where this stops being right

• This page cannot tell you which method was used. That is not a limitation to work around; it is the true state of the question. Four documented methods produce four different letters from one score, and the input that picks between them lives in your instructor's head. Every figure here reads “if this is what happened”.
• Many instructors curve by hand, to no method at all. Moving the cut-offs down until the distribution looks right is common, and it is not any of the four formulas above. If your instructor said “an 85 will be an A on this one”, they changed the cut-off table, not the scores — that's the Grade Scale Converter, not this page.
• Some institutions forbid mandating a curve, and some require one. Alberta's policy rules out mandating grades on a curve or a historic distribution; Michigan State's law school requires a numeric target mean. Most universities publish nothing either way, which leaves the decision entirely with the instructor.
• Class statistics you weren't given can't be reverse-engineered. Knowing your own curved and uncurved score identifies a line only if you already know it was a linear method. Two of the four fit almost any single pair of numbers.
• Your instructor and registrar own the real grade. This page computes what each documented method implies, and nothing more.

Sources

The arithmetic needs no authority. What needs citing is the claim the page is built on: that these methods are documented, that institutions take opposite positions on whether curving is even allowed, and that none of them requires the method to be disclosed to you.

Mehvar, R. (2025). A Practical Guide to Grade Adjustment or Curving for Pharmacy and Other Professional Health Programs. Pharmacy, 13(1), 4. Gives the mean-and-spread method as “Adjusted Score = Adjusted Mean + (Adjusted SD/Raw SD) × (Raw Score − Raw Mean)”, notes that an SD ratio of 1 reduces it to a uniform shift, and warns that curving “should not be viewed as a simple remedy to increase the grades when a large number of students perform poorly.”

Michigan State University College of Law, Grade Curve Policy: a mandatory curve with a “target mean of 3.00” for first-year classes and 3.33 for upper-level ones, permitted variances of ±0.07 for larger classes and ±0.17 for classes of twenty or fewer, and “no more than 70% of grades awarded in any class may be B+ (3.33), B (3.00), B− (2.67).” A published curve that can lower grades as readily as raise them.

University of Alberta, Assessment and Grading Policy (UAPPOL): “Grades in any course, examination or other academic assessment shall not be mandated on the basis of a curve or historic distribution of student grades,” and “the distribution of grades shall not be predetermined by any system of quotas that requires a certain number or percentage of grades at a particular level.” The opposite pole from a mandatory curve, published as policy.

Between those two poles sit most universities, which publish nothing at all about curving. That silence is why this page shows four answers instead of one.

Last reviewed: August 2026