P-Value Calculator
Convert a z, t or chi-square test statistic into a p-value, one- or two-tailed.
About the P-Value Calculator
Choose the test statistic (z, t or χ²), enter its value, the degrees of freedom for t and χ², and whether the test is one- or two-tailed. The calculator gives the p-value and whether it's significant at 5% and 1%.
The p-value is the probability of getting a result at least as extreme as yours if the null hypothesis were true. A small p-value (commonly below 0.05) suggests the data are unlikely under the null hypothesis.
The formula
Two-tailed p = 2 × min(F(x), 1 − F(x))
- F
- cumulative distribution of z, t or χ²
Worked example
A test statistic of 2.1, two-tailed
- As a z: p = 0.0357, significant at 5%
- As a t with 10 degrees of freedom: p = 0.0621, not significant
- Small samples need a bigger statistic for the same p
Questions people ask
Does p < 0.05 prove my hypothesis?
No. It indicates the data are unlikely under the null; it doesn't measure the size or importance of an effect.
One- or two-tailed?
Two-tailed unless you decided before seeing the data that only one direction matters.
Where do I get the test statistic?
From your test: the T-Test, Chi-Square or Z-Score calculators all give one.