How to use the Z-score Calculator
The z-score calculator shows how many standard deviations a value is from the mean and its percentile.
What you need to enter
- Value (x)
- Mean (μ)
- Standard deviation (σ)
The formula
z = (x − μ) ÷ σ. The percentile comes from the normal distribution.
Worked example
Using the default values in the calculator:
- Value (x): 85
- Mean (μ): 70
- Standard deviation (σ): 10
| Z-score | 1.5 |
| Percentile (below) | 93.319% |
| Above | 6.681% |
Tips for better results
- Use it to compare values from different scales.
- Assume roughly normal data.
Common mistakes to avoid
- Using the wrong σ.
- Mixing sample and population.