How to use the z-score calculator
Standardise a value and find its percentile. Enter value, mean, standard deviation in the fields above; the z-score, percentile, probability above are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- x — Value
- mu — Mean
- s — Standard deviation
Worked example
With value = 85, mean = 70, standard deviation = 10, the calculator gives z-score ≈ 1.5; percentile ≈ 93.31928 %; probability above ≈ 6.680723 %.
Frequently asked questions
What is the formula for the z-score calculation?
Z-score = (x-mu) / s. Percentile (%) = 100 × ncdf([Z-score]). Probability above (%) = 100 × (1-ncdf([Z-score])). Here x is value, mu is mean, s is standard deviation.
What inputs do I need for the z-score calculator?
You need value, mean, standard deviation. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.