Z-Score Calculator
Find the z-score for any value, plus its percentile and p-values. Or work backwards from a percentile to the value you need.
Don't know the mean and standard deviation? Get them from your data with the standard deviation calculator.
How it works
What is a z-score?
A z-score tells you how many standard deviations a value is above or below the mean: z = (x − μ) ÷ σ. A z-score of 1.5 means the value is 1.5 standard deviations above average; −2 means two below.
What's the percentile?
For normally distributed (bell-curve) data, the percentile is the share of values below yours. A z-score of 0 is the 50th percentile; z = 1.96 is about the 97.5th. The shaded area on the curve shows it.
Which p-value should I use?
Left-tailed is the chance of a value at or below yours, right-tailed at or above, and two-tailed is the chance of a value at least this far from the mean in either direction. Two-tailed is the usual choice in hypothesis tests unless you're testing a specific direction.
Common z-scores
90% confidence: ±1.645 · 95% confidence: ±1.960 · 99% confidence: ±2.576.