Z-Score Calculator
Standard score, percentile and tail probabilities.
Enter your values
ⓘ Live results
Results
- Z-score
- 2.1333
- Percentile
- 98.36%
- Probability above this value
- 1.645%
- Two-tailed p-value
- 3.2897%
Working
- 1z = (132 − 100) ÷ 15 = 2.1333
Quick answer
A z-score is how many standard deviations a value sits from the mean: z = (x − μ) ÷ σ.
z = (x − μ) ÷ σ
How to use the Z-Score Calculator
- 1Enter the raw value.
- 2Add the population mean and standard deviation.
- 3Read the z-score and percentile.
Worked example
Using the values the calculator loads with:
Inputs
- Value (x)132
- Mean (μ)100
- Standard deviation (σ)15
Results
- Z-score2.1333
- Percentile98.36%
- Probability above this value1.645%
- Two-tailed p-value3.2897%
- z = (132 − 100) ÷ 15 = 2.1333
Frequently asked questions
What z-score is significant?
At the conventional 5% two-tailed level, |z| above 1.96 is significant; 2.58 corresponds to the 1% level.
Can a z-score be negative?
Yes — it simply means the value sits below the mean.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.