Z Score Calculator – Standard Deviations from Mean
Free z-score calculator: enter a value, mean, and standard deviation to find how many standard deviations the value is from the mean. No sign-up.
Z Score Calculator
Convert a value to a Z score (standard score) using the mean and standard deviation.
How the z-score is calculated
z = (value − mean) / standard_deviation
Standard deviation must be greater than zero. The z-score is unitless and allows comparison across different scales. For standard deviation from raw data, use our standard deviation or variance calculator.
When to use a z-score
Z-scores standardize values so you can compare them across different distributions. A test score of 85 means little without context; a z-score of 1.5 means the score is 1.5 standard deviations above the mean. Z-scores are used in hypothesis testing, quality control, and when working with the normal distribution to find percentiles.
In a normal distribution, about 68% of values fall within z = ±1, 95% within z = ±2, and 99.7% within z = ±3. Use our standard deviation calculator to compute mean and SD from raw data, then use this z-score calculator to convert individual values to z-scores.