About the z-score calculator
A z-score tells you how many standard deviations a value is above or below the mean. In a normal distribution, it also gives the percentage of values below that point.
How to use this calculator
- Enter the value, the mean, and the standard deviation.
- Read the z-score and percentile.
Worked examples
- z = (85 − 70) ÷ 10 = 1.5
- Φ(1.5) ≈ 0.9332
z = 1.5, about the 93rd percentile.
Measurement guidance
Sample or population
Use the standard deviation that matches your data: population or sample.
Frequently asked questions
What does a negative z-score mean?
The value is below the mean.
Is a z-score of 2 rare?
In a normal distribution, about 2.3% of values are above z = 2.