Z-Score Calculator (with Percentile)
Z-score calculator: standardise a value with the mean and standard deviation, and get its percentile.
z = x − μσ
How to use this calculator
- Choose the quantity you want under “Solve for”.
- Type the known values and pick their units: any combination works.
- The result updates as you type. Open “Show the steps” to see the substitution.
z = (x − μ)/σ tells how many standard deviations a value lies from the mean.
For normally distributed data the calculator also gives the percentile, the share of values below x.
Formula
z = x − μσ
| Symbol | Quantity | Units |
|---|---|---|
| x | Value | — |
| μ | Mean | — |
| σ | Standard deviation | — |
| z | Z-score | — |
Worked example
Given: x = 130 · μ = 100 · σ = 15
z = x − μσ
Result: z = 2
Frequently asked questions
IQ 130 with mean 100 and SD 15?
z = 2, about the 97.7th percentile.