This free online z-score calculator tells you how many standard deviations a value is above or below the mean of a data set. It's widely used in statistics to standardize scores and compare data points from different distributions.
How to Use the Z-score Calculator
Enter the data point you want to standardize in the "Value (x)" field.
Enter the data set's average in the "Mean (μ)" field.
Enter the data set's spread in the "Standard Deviation (σ)" field.
Click "Calculate" to see the z-score and a plain-language interpretation.
Frequently Asked Questions
It uses z = (x − μ) / σ, where x is your value, μ is the mean, and σ is the standard deviation. For example, if x = 70, μ = 60, and σ = 5, then z = (70 − 60) / 5 = 2.000, meaning the value is 2 standard deviations above the mean.
A negative z-score means your value is below the mean. The calculator reports the direction as "above" or "below" the mean based on the sign of the result, along with how many standard deviations away it is.
Since the standard deviation is the denominator in the z-score formula, a value of zero would make the calculation undefined, so the calculator shows "Standard deviation cannot be zero" instead of a result.
Yes, it's completely free with no sign-up required.