Z Z-Score Calculator
Calculate the z-score (standard score) of a value and find its corresponding percentile in a normal distribution.
Values
Your Result
How the Z-Score Calculator Works
A z-score tells you how many standard deviations a value is from the mean of its distribution. Z-scores are used to compare values from different normal distributions and to find percentile ranks.
Formula
Percentile = Φ(z) × 100, where Φ is the standard normal cumulative distribution function
Frequently Asked Questions
What does a negative z-score mean?
A negative z-score means the value is below the mean. A positive z-score means it's above the mean. A z-score of 0 means the value equals the mean.
How is percentile related to z-score?
The percentile shows the percentage of values in a normal distribution that fall below your value. For example, a z-score of 0 corresponds to the 50th percentile.
How accurate is the percentile calculation?
This calculator uses a well-known polynomial approximation of the standard normal cumulative distribution function, accurate to about 7 decimal places — more than enough precision for practical use.