Z score calculator

See how far a value is above or below the mean.

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Z score calculator processes your input in this browser. Inputs and results are excluded from analytics. Recent tools save tool names, visit counts and last-visit times. Saved tools store only their names. Draft saving is optional and stays on this device; delete saved text with the draft controls. Loading text from a URL is optional and contacts that server; its URL and your IP address are visible to the server. An optional “Use in” action keeps a handoff in this tab. The next tool removes it on arrival and ignores it if more than a minute has passed.

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Observed value

Mean

More inputs and assumptions

Standard deviation

Answer

…

Z-score = (observed value − mean) ÷ standard deviation.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Step-by-step calculation

Inputs are substituted below. Each line evaluates the next operation; intermediate values are displayed to 12 significant digits while the calculation uses full precision.

Saved scenario

Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

The standard deviation must be positive. A z-score measures distance in standard deviations; it does not establish a normal distribution.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

Scratch calculator

Check another calculation

Use +, −, ×, ÷, parentheses and %. A percentage is divided by 100. This does not change the main tool.

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Updated 2026-09-26

Using Z score calculator

Z-score = (observed value − mean) ÷ standard deviation.

The standard deviation must be positive. A z-score measures distance in standard deviations; it does not establish a normal distribution.

Next: Percentile calculator

A worked example

With observed value = 85, mean = 70, standard deviation = 10, the z-score is 1.5.

Next: Standard error calculator

Before you use the result

The standard deviation must be positive. A z-score measures distance in standard deviations; it does not establish a normal distribution.

Example results for observed value

These examples use Mean: 70; Standard deviation: 10. They are reference calculations, not recommended settings.

Observed value	Z-score
42.5	-2.75
85	1.5
170	10

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ToolOctopus. “Z score calculator.” Updated 2026-09-26. https://tooloctopus.com/z-score-calculator.

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