Z Score Calculator
A z score says how far a value sits from the average, measured in standard deviations. Positive means above the average, and negative means below it.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
The z score is the value minus the average, divided by the standard deviation.
The share below assumes the values follow a normal bell curve, which many measurements roughly do. If the data is strongly skewed, the share will be less reliable.
Worked example
A value of 85 against an average of 70, with a standard deviation of 10, gives a z score of 1.5, with about 93.3% of values below it.
Questions
What is a normal bell curve?
It is a symmetric curve where most values sit near the average. Heights and test scores often roughly follow one.
Is a z score of 2 unusual?
It is well above the average, and few values sit that high on a normal curve. Whether that matters depends on your data.
Where do I get the standard deviation?
Use the standard deviation of your group, or a figure from a source you trust. The standard deviation calculator can work it out from a list of numbers.
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