z score is a measurement of how many standard deviations above the mean or below the mean.

for example in the below image the value 2.9 is 2 standard deviations away from the mean of 2.5, so 2.9 has a z-score of 2.

3.1 has a z-score of 3.

## Z-score formula

z = (x – μ) / σ

Z = standard score

x = observed value

μ = mean of the sample

σ = standard deviation of the sample