Find the z-score of a value and the percentile it corresponds to on a normal distribution. Enter the value, mean, and standard deviation.
Usage Tip
Roughly: z of 1 is the 84th percentile, z of 2 the 98th. About 95 percent of data lies within z of plus or minus 2.
Percentile from the standard normal distribution
On a normal distribution it maps directly to a percentile.
A positive z is above the mean, negative is below.
The percentile assumes a normal distribution.
A z-score tells you how many standard deviations a value sits above or below the mean. It is found by subtracting the mean from the value and dividing by the standard deviation. A z-score of 0 is exactly average, positive scores are above average, and negative scores are below.
Z-scores let you compare values from different scales, such as test results with different averages and spreads. The percentile shown assumes the data follows a normal distribution, so it is less reliable for skewed data. Values with a z-score beyond about 2 or 3 in either direction are unusual and are often examined as possible outliers.