Calculate the z-score (standard score) of a value, along with its percentile rank and the probability of observing a value above or below it in a normal distribution.
How it works
- Enter the raw value (x) you are analyzing.
- Input the population or sample mean.
- Provide the standard deviation to calculate the precise z-score and probability.
Frequently asked questions
What does a z-score tell me?
How far a value is from the mean, in standard deviations. A z of +2 means the value is 2 standard deviations above average — higher than ~97.7% of values.
What is a normal z-score range?
About 68% of values fall within ±1, 95% within ±2, and 99.7% within ±3. Z-scores beyond ±3 are rare.
Can z-scores be negative?
Yes — a negative z-score means the value is below the mean. The sign indicates direction; the magnitude indicates distance.