What is a percentile?

A percentile is the share of a distribution that falls below a given value. The 70th percentile means about 70% of values are below yours and about 30% are above — it describes rank within a group, not a raw score.

Is a higher percentile always better?

For most measures reported this way — test scores, growth charts, rankings — yes, a higher percentile means you rank above more of the group. But check what is being measured: for something like reaction time or error rate, a lower raw value (and so a different percentile framing) can be the better outcome, so read the units, not just the number, before assuming higher is better.

How is a percentile different from a percentage?

A percentage (like 85% correct) describes a raw score out of the total possible. A percentile (like the 85th percentile) describes rank relative to everyone else's scores. The two can be very different numbers on the same test — a percentile depends on how everyone else did, not just on your own score.

Percentile Calculator

Free percentile calculator: find what percentile a score falls at, or find the score at a given percentile, for a normal distribution — with the z-score and formula shown.

Direction Mean Standard deviation

Percentile A number between 0 and 100 — for example, 90 for the 90th percentile.

z = 1.2816, percentile = 90, score = 119.2233

Score from a percentile, step by step

z for the 90th percentile = 1.2816.

Score = mean + z × SD = 100 + 1.2816 × 15 = 119.2233.

What a percentile means

A percentile tells you what share of a distribution falls below a given value. Being at the 85th percentile means about 85% of values in the distribution are below yours (and about 15% are above) — it is a statement about rank within the group, not a raw score or a percentage correct. This calculator finds the percentile for a score, or the score at a given percentile, for a normal distribution defined by a mean and standard deviation.

Percentile vs. percent correct

The most common mix-up is treating a percentile like a percentage score. The 85th percentile on a standardized test does not mean the student answered 85% of questions correctly — it means they scored better than about 85% of the people who took the test. A student could be at the 85th percentile with a raw score of 60% correct if the test was hard and most people scored lower, or with 95% correct if the test was easy and most people scored close to that. Percentile is about rank relative to a group; percent correct is about the raw score itself — they answer different questions and can move independently of each other.

Worked example

Say a standardized test's scores are normally distributed with a mean of 100 and a standard deviation of 15, and a student wants to know their score at the 90th percentile. The z-score for the 90th percentile is about 1.2816, so their score is 100 + 1.2816 × 15 ≈ 119.2. Read the other way: a student who scored 119 on that same test sits at about the 90th percentile — meaning they outperformed roughly 90% of test-takers.

Common percentile milestones

Percentile milestones show up often in real reporting — the 50th percentile is the median, right in the middle of the distribution; the 25th and 75th percentiles (the quartiles) bracket the middle half; and standardized tests, growth charts, and salary surveys routinely report where an individual value falls among percentiles like the 10th, 25th, 50th, 75th, and 90th. A percentile close to 50 is unremarkable — near the center of the pack. A percentile in the single digits or the high 90s marks a genuinely unusual value relative to the rest of the distribution.

How to use it

Choose the direction: percentile → z-score and score, or score → z-score and percentile.
Enter the mean and standard deviation of the distribution.
Enter the percentile you want the score for (or the score, in the reverse direction).
Read the z-score, score, and the step-by-step working below the shaded curve.
Download the chart as PNG, SVG, or PDF, or export the numbers as CSV.

FAQ

What is a percentile?: A percentile is the share of a distribution that falls below a given value. The 70th percentile means about 70% of values are below yours and about 30% are above — it describes rank within a group, not a raw score.
Is a higher percentile always better?: For most measures reported this way — test scores, growth charts, rankings — yes, a higher percentile means you rank above more of the group. But check what is being measured: for something like reaction time or error rate, a lower raw value (and so a different percentile framing) can be the better outcome, so read the units, not just the number, before assuming higher is better.
How is a percentile different from a percentage?: A percentage (like 85% correct) describes a raw score out of the total possible. A percentile (like the 85th percentile) describes rank relative to everyone else's scores. The two can be very different numbers on the same test — a percentile depends on how everyone else did, not just on your own score.