Numbers
Calculateur de score Z
Used by developers, writers, and creators worldwide.
A z-score calculator tells you how far a value sits from the mean, measured in standard deviations. Enter the value, the mean of the distribution, and the standard deviation, and it computes the z-score as the value minus the mean divided by the standard deviation, states how many standard deviations above or below the mean the value lies, estimates the percentile under a normal distribution, and flags whether the value is unusual. Z-scores let you compare data points from different scales on a common footing, which is why they are central to standardised tests, quality control, anomaly detection, and statistics coursework. Students use the tool to check homework, analysts to spot outliers, and anyone comparing scores across different exams or measurements. The approximate percentile, from a standard normal model, turns the z-score into an intuitive ranking. Use it to standardise a value or convert a raw score into a percentile.
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How to use
- Choose your options above
- Click Generate
- Copy your result
Detailed instructions
- Enter the value you want to standardise.
- Enter the mean of the distribution.
- Enter the standard deviation.
- Click Generate to compute the z-score.
Use Cases
- •Standardising a value to compare across scales
- •Finding how unusual a data point is
- •Estimating a percentile from a raw score
- •Spotting outliers in quality control
- •Checking z-score statistics homework
Tips
- →A positive z-score is above the mean, negative below.
- →About 95% of normal data fall within two standard deviations.
- →Z-scores let you compare different scales fairly.
- →The percentile assumes a normal distribution.
FAQ
how is the z-score calculated
It is the value minus the mean, divided by the standard deviation. A positive z-score means the value is above the mean and a negative one means below, with the size telling you how many standard deviations away it lies.
what does the percentile assume
The percentile assumes the data follow a normal bell-shaped distribution and uses a standard accurate approximation of its curve. If your data are far from normal, treat the percentile as a rough guide rather than an exact figure.
when is a value considered unusual
A common rule of thumb treats a z-score beyond plus or minus two as unusual, since about 95 percent of normally distributed values fall within two standard deviations of the mean. This is a guideline for an educational estimate, not a strict cutoff.
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