Z-Score Calculator
Z-Score
0.5
Percentile
69.146246%
P(Z < z): left tail
0.691462
P(Z > z): right tail
0.308538
P(|Z| > |z|): two-tailed
0.617075
FAQ
Standard normal distribution
What is z-score?
Number of standard deviations a value X is from the mean μ. z = (X - μ) / σ. Lets you compare values from different distributions or compute probabilities.
What is p-value?
Probability of observing a value at least as extreme as the one obtained, assuming the null hypothesis is true. p < 0.05 typically indicates statistical significance.
What is a z score?
It is the number of standard deviations that separate a value from the mean. It lets you compare measurements coming from different distributions, by bringing them all onto one scale.
What does the p value tell me?
It says how likely it is to see a value this extreme if the starting hypothesis were true. Below the threshold you have fixed, usually five per cent, the result is called significant.
What is the difference between one tail and two tails?
With one tail you look at the departure in a single direction, with two tails in both. The two tailed test is the more cautious one, because it splits the threshold between the two sides.