Statistics & Probability
Intermediate

Z-Score

Number of standard deviations a value is from the mean.

Formula

z=x−μσz = \frac{x - \mu}{\sigma}

Variables

xValue
\muMean
\sigmaStandard deviation

Example

A score of 85 with mean 75, σ = 5: z = (85−75)/5 = 2 (two SDs above average).

Did You Know?

A z-score tells you how many standard deviations a value sits from the mean — the language of "grading on a curve".

z-scorenormalization