๐P-Value Calculator
Convert a z, t, chi-square, or F statistic into a p-value, with a shaded distribution graph.
Free P-Value Calculator
Already have your test statistic and just need the p-value? Our free P-Value Calculator converts a z-score, t-statistic, chi-square statistic, or F-statistic into a p-value instantly โ with a shaded distribution graph so you can see exactly what's being measured.
Choose your statistic type, enter the value and degrees of freedom (where needed), pick left-tailed, right-tailed, or two-tailed, and get an accurate p-value along with significance flags at the common 0.05, 0.01, and 0.001 thresholds. No more flipping through printed distribution tables or interpolating between rows.
Built for students and researchers who've already run a test and need the final piece โ an accurate p-value with a clear visual. Free, no sign-up, no limits. See the About page or the FAQ for more.
About the P-Value Calculator
Features
Four statistic types
Z, T, chi-square, and F, each with the appropriate degrees-of-freedom inputs.
Tail selection
Left, right, or two-tailed for z and t; chi-square and F default to right-tailed as is standard.
Shaded distribution graph
A live canvas plot of the relevant distribution with the p-value region shaded.
Accurate CDF implementations
Uses the incomplete beta and incomplete gamma functions for the t, chi-square, and F distributions.
Significance flags
Instantly see whether your result is significant at ฮฑ = 0.05, 0.01, and 0.001.
Frequently Asked Questions
What is a p-value?
The probability of observing a result as extreme as (or more extreme than) yours, assuming the null hypothesis is true.
Which statistic type should I choose?
Match it to the test you ran: z for a z-test, t for a t-test, chi-square for a goodness-of-fit/independence test, F for ANOVA or a variance-ratio test.
What's the difference between one-tailed and two-tailed?
A one-tailed test only considers extremity in one direction; two-tailed considers both, and generally gives a larger p-value for the same statistic.
Do chi-square and F tests use tails differently?
Yes, they're typically evaluated as right-tailed tests since their statistics are always non-negative; the calculator reflects this.
What degrees of freedom do I enter?
For t and chi-square, one df value; for F, two (numerator and denominator degrees of freedom).
What does a small p-value mean?
Conventionally, p < 0.05 is considered statistically significant, meaning the observed result is unlikely under the null hypothesis โ though significance thresholds depend on your field and study design.
Does it show a graph?
Yes, a shaded curve of the relevant distribution highlights the area corresponding to your p-value.
How accurate is the calculation?
It uses precise CDF approximations for each distribution, matching standard statistical tables to several decimal places.
Is my data stored?
No, everything is calculated client-side in your browser.
Is it free?
Yes, completely free with no sign-up or limits.