P-value Calculator guide
P-value Calculator: Z, t, Chi-Square and F Tests
Use our p-value calculator to find the p-value from a z, t, chi-square or F test statistic, for one or two-tailed tests.
By the AllCalculator editorial teamUpdated 16 October 20261 min read
The p-value is at the heart of hypothesis testing. It tells you how surprising your result would be if there were really no effect. Our P-value Calculator turns a test statistic into a p-value.
How to use the calculator (P-value Calculator)
- Choose the test statistic: z, t, chi-square or F.
- Enter its value and the degrees of freedom if needed.
- Choose a two-tailed, right-tailed or left-tailed test.
- Set your significance level (α), usually 0.05.
What the p-value means
The p-value is the probability of getting a result at least as extreme as yours if the null hypothesis is true.
- p < α: the result is statistically significant, so you reject the null hypothesis.
- p ≥ α: you don't have enough evidence to reject it.
Which test?
| Test | Used for |
|---|---|
| Z | Large samples or known standard deviation |
| t | Comparing means with small samples |
| Chi-square | Counts in categories, such as survey answers |
| F | Comparing variances, and ANOVA |
A worked example
With the calculator's default settings, a z statistic of 2.1 in a two-tailed test gives p = 0.0357. That's below 0.05, so the result is significant at the 5% level, but not at 1%.
Frequently asked questions
One-tailed or two-tailed?
Use two-tailed unless you decided in advance to test for an effect in only one direction.
Does a small p-value mean a big effect?
No. With a huge sample, tiny effects can be significant. Report the effect size and a confidence interval as well.
Is 0.05 a magic number?
It's a convention, not a rule. Many fields now report the exact p-value instead.
For z-scores and percentiles, use our Z-score Calculator.
Sources and further reading
- NIST/SEMATECH e-Handbook of Statistical Methodsitl.nist.gov
- ONS: Uncertainty and how we measure it for our surveysons.gov.uk
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.