Z-Score Calculator
z = (x − mean) ÷ SD. Click any i for detail.
Distribution
x
i
x
The value you are standardizing. |
|
|---|---|
Mean (μ)
i
Mean
Population or sample mean you are measuring against. |
|
Standard deviation (σ)
i
SD
Must not be 0. |
How to use this calculator
- Enter x, mean, and SD.
- Read z.
- Mean/median/mode builds SD from a list.
- IQ-style 15-point SDs are just an example default.
Results explained
z says how many standard deviations x sits above (positive) or below (negative) the mean.
Quick reference: z
x = 115, mean 100, SD 15 → z = 1.
| Item | Detail |
|---|---|
| z = 0 | x equals the mean |
| z = ±1 | One SD away |
| List stats | Mean median mode calculator |
| % difference | Two numbers, no SD |
A z-table / tail probability is not printed.
How the estimate is built
z = (x − μ) / σ.
Example scenario
115 vs mean 100, SD 15 → z = 1.00.
FAQ
Sample vs population SD?
Enter whichever SD your problem uses.
Percentile?
Needs a normal assumption and a table — not here.
Grading curve?
Same formula if you have class mean and SD.