What is a percentile rank?

A percentile rank is the percentage of scores that fall at or below yours. Being in the 90th percentile means you scored higher than about 90 percent of the group. It describes relative standing, not the percentage of questions you answered correctly.

A Z-score expresses how many standard deviations your score is above or below the mean. A Z of plus one means you scored one standard deviation above average, which is roughly the 84th percentile under a normal curve.

How accurate is this estimate?

It assumes scores follow a normal bell curve. Real exam results are often close to normal for large classes but can be skewed for small or capped tests, so treat the percentile as an approximation rather than an exact rank.

Where do I find the mean and standard deviation?

Instructors frequently publish the class average and spread with results, and learning platforms often display them. If only the mean is given, you can estimate the standard deviation from the range, but accuracy will suffer.

Can the percentile exceed 99 or fall below 1?

Yes. Extreme scores produce percentiles very close to 100 or 0. The tool reports these as high or low percentiles, reflecting that almost everyone scored below or above you respectively.

Exam Score Percentile Calculator

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See how your score ranks against the class

A raw mark alone says little about how well you did relative to others. This calculator places your score on the class distribution: it converts your mark into a Z-score, then into a percentile that tells you roughly what fraction of students you outperformed. All it needs is your score, the class mean, and the standard deviation.

How it works

First it computes the Z-score, the number of standard deviations between your score and the mean:

z = (score - mean) / standardDeviation

It then maps that Z-score to a percentile using the cumulative distribution function of the standard normal curve, evaluated with a high-accuracy error-function approximation. A Z of 0 maps to the 50th percentile, a Z of plus one to about the 84th, and a Z of minus one to about the 16th.

Example and notes

If you scored 78 on an exam with a class mean of 65 and a standard deviation of 10, your Z-score is 1.3, placing you near the 90th percentile. The model assumes a normal distribution, which holds best for large classes. For small groups or exams where many students hit the ceiling, the percentile is an estimate and the true rank may differ.