Z-score Calculator

Use this free z-score calculator to standardize a value from its mean and standard deviation, see whether it is above or below average, and estimate percentile.

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Illustration for Z-score Calculator showing calculate a z-score and approximate standard normal percentile. — Z-score Calculator artwork matches the live tool workflow: calculate a z-score and approximate standard normal percentile. Use it with the calculator, examples, and result notes. View in the smoke-kawaii gallery

Inputs to check Example numbers Copyable answer Tab-only history

Value xMeanStandard deviation

Z-score1.5

Percentile: 93.3192769023%
Distance: Above mean
Mean: 70

How to use the Z-score Calculator

Enter the value, mean, and standard deviation.
Press Calculate z-score to standardize the value.
Review whether the value is above or below the mean and the approximate normal percentile.
Use examples, recent answers, or copy the result while checking statistics work.

What people use it for

Standardize a value using mean and standard deviation.

See how many standard deviations a value is above or below average.

Estimate a percentile under the standard normal curve.

Check statistics, normal distribution, and study examples.

Quick examples

Above average

x=85, mean=70, SD=10

z = 1.5

At the mean

x=70, mean=70, SD=10

z = 0

Below average

x=55, mean=70, SD=10

z = -1.5

Need the guide or a nearby tool?

Need a slower walkthrough, a related calculator, or the full library? These links keep you close to the task you started.

How to use the Z-score Calculator See slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
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Frequently asked questions

Quick answers about formulas, inputs, examples, result copying, and private in-browser history.

What is a z-score?

A z-score tells how many standard deviations a value is above or below the mean.

What formula does the calculator use?

It uses z = (x - mean) / standard deviation, then reports whether the value is above or below the mean.

What do the main Z-score Calculator inputs mean?

The main inputs are the numbers, operation, mode, or known values the calculator needs. Keep units consistent, enter percentages the way the page label shows, and use the examples as a quick check before trusting the answer.

How should I read the Z-score Calculator answer?

Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.

What should I double-check before trusting the Z-score Calculator?

Check units, signs, rounding, and the selected mode before copying the answer. If the number feels weird, rerun one of the examples first, then put your own values back in slowly.

What does a negative z-score mean?

A negative z-score means the value is below the mean. A positive z-score means it is above the mean.

What does the percentile estimate mean?

The percentile estimates the area to the left of the z-score on a standard normal curve.

Can the standard deviation be zero?

No. A z-score divides by standard deviation, so the standard deviation must be greater than zero.

Is my z-score history private?

Yes. Recent z-score answers stay only in the current browser tab while you use the page. They are not sent to a server.