Grade Curve Calculator: Add Points or Scale to 100

How to use it

Choose the Curve method and fill in the field that appears: Points to add, or Target mean and Target standard deviation.
Type one score per line in Scores. Lines that are not scores are listed under Lines not read.
Read New mean, then the Scores before and after table.
Compare Mean, Median and Standard deviation in the summary table before and after the curve.

The three curve methods

Add points:  new = score + points

Scale to 100:  new = score × 100 ÷ highest score

Target:  new = target mean + (score − mean) ÷ sd × target sd

Add points: each new score is the old score plus the points. The order of the scores and the differences between them stay the same.
Scale the top score to 100: each new score is the old score times 100 divided by the highest old score. The highest score becomes 100, and the others move up in proportion.
Target mean and standard deviation: each new score is the target mean plus z times the target standard deviation, where z is the score's distance from the mean in standard deviations, (score − mean) ÷ standard deviation. The new list has the target mean and spread.

Mean, median and standard deviation

The median is the middle score when the scores are sorted. With an odd count it is the middle value; with an even count it is the mean of the two middle values (Wikipedia, Median).

The standard deviation is calculated as the sample value: the squared distances from the mean are added, divided by n − 1, and the square root is taken. The article on standard deviation recommends the n − 1 form for an estimate from a sample, which is what a class of scores is.

What a curve does not decide

The tool does not cap scores at 100 and does not round them to a grade letter. Your school's rules decide whether a curve may pass 100 and how the new scores become grades.
A target-method curve sets the new mean and spread from this list alone, so a class that did very well is still moved to the target mean. The method changes the scale of the scores; it does not measure what the students learned.
Wikipedia's article on grading on a curve describes the bell-curve idea behind the target method; it gives no fixed rule for adding points or scaling, which this tool applies as written.

Worked example: scores 50, 60, 70, 80, 90 on a target of 70 and 10

The mean of these five scores is 70 and the sample standard deviation is √250 = 15.81. The score 50 is 20 below the mean, so z = −20 ÷ 15.8114 = −1.2649, and its new score is 70 + (−1.2649 × 10) = 57.35. The same step gives 63.68 for 60, 70 for 70, 76.32 for 80 and 82.65 for 90. The new mean is 70 and the new standard deviation is 10.

Measure	Before	After
Mean	70.00	70.00
Median	70.00	70.00
Standard deviation	15.81	10.00

Frequently asked questions

Does adding points change the order of the scores?

No. Adding the same number to every score moves each one by the same amount, so the order and the gaps between scores stay the same.

Why is the standard deviation divided by n − 1?

The scores are a sample of the students' ability, and dividing by n − 1 gives the usual estimate of the spread from a sample. The standard deviation article on Wikipedia gives this as the common choice.

What happens if all the scores are the same?

The standard deviation is zero, so the target method cannot spread the scores. The tool says so. The points and the scale methods still work.

Can a curve give a score above 100?

Yes, the points method and the target method can, and the tool does not cap them. Apply your school's cap after the curve if its rules need one.

Are my scores sent anywhere?

No. The curve is calculated in your browser. The scores are not stored and are not sent to the site.

Sources

Figures and text last checked on Tuesday, November 10, 2026.

Result

Lines not read