Math & Statistics

What Is a Z-Score?

A z-score, or standard score, shows how many standard deviations a value is from the mean. Z = (value − mean) ÷ standard deviation. A z-score of 0 is exactly at the mean, positive values are above it, and negative values are below it.

Example

A test score of 85 in a class with mean 70 and standard deviation 10 has a z-score of 1.5.

Use

Z-scores let values from different scales be compared and are used to spot outliers.

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📉 Standard Deviation Calculator Sample and population standard deviation and variance, with a step table. Calculate → 📊 Average Calculator (Mean, Median, Mode) Get the mean, median, mode, range, and sum of any list of numbers. Calculate →

🔗 Related Terms

Standard Deviation Normal Distribution Outlier Mean (Average)

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Last updated: September 27, 2026. This definition is for general educational purposes only. It is not financial, investment, tax, legal, or medical advice, and it does not recommend any product or course of action. For decisions about your own situation, consult a qualified professional.