Test Statistic to P Value Calculator
Turn a t test statistic and degrees of freedom into p-values, including two-tailed and one-tailed reference rows.
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Result
Enter values above and click Calculate to see your result.
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Formula
How it works: Computes tail probabilities from the same t statistic so you can compare one-sided and two-sided interpretations.
Worked Example
Converting Test Statistics to P-Values
This calculator takes a single t statistic and degrees of freedom and returns all three p-value interpretations: two-tailed, upper one-tailed, and lower one-tailed. This lets you see the full picture and choose the correct value for your specific hypothesis test.
- Two-tailed p: for non-directional hypotheses testing whether a parameter differs from the null in either direction
- Upper one-tailed p: for hypotheses predicting the parameter is greater than the null value
- Lower one-tailed p: for hypotheses predicting the parameter is less than the null value
- All three values come from the same underlying t distribution. They differ only in which tail area is reported
Choose your p-value based on the hypothesis you specified before collecting data. Never select the tail type that gives you the smallest p-value after seeing results.
You can also calculate changes using our P Value Calculator, Two-Tailed P Value Calculator, One-Tailed P Value Calculator or Test Statistic Calculator.
Frequently Asked Questions
Which p-value row should I report?
Use the two-tailed value for a two-sided alternative hypothesis. Use upper or lower one-tailed only if your hypothesis was directional and specified before data collection.
Can I enter a z statistic instead of t?
This tool uses the Student t distribution. For large degrees of freedom (above 30), t and z produce nearly identical p-values. For exact normal z-based p-values, use a z-score calculator.
Why does the same t give different p-values?
The three values represent different areas under the t distribution curve. Two-tailed sums both tails. Upper one-tailed uses only the right tail. Lower one-tailed uses only the left tail. The total probability is the same, just divided differently.
What does a very small p-value mean?
A very small p-value (e.g., less than 0.001) means the observed t statistic would be extremely unlikely under the null hypothesis. This provides strong evidence against the null, though it does not prove the alternative hypothesis is true.
How can I put this Test Statistic to P Value Calculator on my blog or website?
Yes, the Test Statistic to P Value Calculator is fully embeddable. Tap "Embed" above to configure appearance and copy the code. It is free to use, works on any platform (HTML, WordPress, CMS), and adjusts to any screen size automatically. Visit calculory.com/services/embed-calculators for the complete guide.
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