Convert a z-score into a one- or two-tailed p-value from the normal distribution.
How this calculator arrives at its answer
Enter a z-score and this calculator returns the p-value β the probability of a result at least as extreme β for a one- or two-tailed test, and whether itβs significant at 0.05.
Itβs a staple of hypothesis testing.
Getting your answer
- Enter your z-score.
- Choose one- or two-tailed.
- Read the p-value and significance.
The calculation
two-tailed p = 2 Γ (1 β Ξ¦(|z|))
one-tailed p = 1 β Ξ¦(|z|)
Try it with these numbers
The calculator opens with a z-score of 1.96. On those figures the p-value is 0.05. Underneath, Significant at 0.05? comes out at Yes and Area beyond z at 0.025. Change any field and every figure updates as you type.
Frequently asked questions
What is a p-value?
The probability of observing a result at least as extreme as yours if the null hypothesis were true. Small p-values cast doubt on the null.
What does significant at 0.05 mean?
A p-value below 0.05 is a common threshold for calling a result statistically significant, though the cutoff is a convention.
One-tailed or two-tailed?
Use two-tailed when you test for any difference, one-tailed when you test in a specific direction.