Z-Score Calculator
Find how many standard deviations a value is from the mean, and its percentile.
What a z-score tells you
A z-score says how many standard deviations a value sits above (positive) or below (negative) the mean. It lets you compare values from different scales, such as test scores from two different exams.
Example
A score of 85 on a test with a mean of 70 and a standard deviation of 10 has a z-score of (85 − 70) ÷ 10 = 1.5. In a normal distribution, about 93.32% of scores fall below it.
Good to know
About 68% of values in a normal distribution lie within z = ±1, about 95% within ±2 and about 99.7% within ±3. The percentile only holds if your data is roughly normal.
Frequently asked questions
Can a z-score be negative?
Yes. A negative z-score means the value is below the mean.
What is a standard deviation?
It is a measure of how spread out values are. You can compute it with the standard deviation calculator.
Last updated