Math July 13, 2026 · 8 Min Read

P-Value Calculator – Guide & Formulas

Calculate p-values for standard normal distribution (Z-score), Student t-distribution, Chi-Square, and F-distribution. Supports one-tailed and two-tailed tests.

Determine statistical significance instantly. This calculator converts test statistics (Z, t, Chi-Square, F) to exact p-values for one-tailed and two-tailed directional hypotheses.

Key Takeaway

Use the free P-Value Calculator to calculate p-values for standard normal distribution (z-score), student t-distribution, chi-square, and f-distribution. supports one-tailed and two-tailed tests. Get instant results with step-by-step explanations.

How to Use the P-Value Calculator

  1. Choose your test statistic type (Z-Score, t-Score, Chi-Square, or F-Ratio).
  2. Enter the score value and any required parameters (like Degrees of Freedom).
  3. Select a significance tail direction: Left, Right, or Two-tailed.
  4. Analyze the resulting probability p-value and the significance conclusion (alpha = 0.05).

The Formula

p-value = cumulative probability tail area(s)

Variable Definitions

  • t: The calculated test statistic value
  • p: The observed level of significance (probability)

Z-Test Significance Verification

An experiment results in a test Z-score of 2.15. Determine if this meets the standard 95% confidence threshold.

  1. Step 1: Set test type to Z-score and input 2.15.
  2. Step 2: Choose two-tailed hypothesis type.
  3. Step 3: Cumulative two-tail probability evaluates to 0.0316.
  4. Step 4: Since 0.0316 < 0.05, the result is statistically significant.

Frequently Asked Questions

What does a p-value represent?

A p-value is the probability of obtaining test results at least as extreme as the observed results, assuming the null hypothesis is completely true.

What is the standard alpha significance level?

The standard threshold is 0.05 (5%). A p-value less than 0.05 indicates strong evidence against the null hypothesis, allowing you to reject it.

Why do two-tailed tests have larger p-values?

Two-tailed tests check for differences in both positive and negative directions, effectively doubling the tail probability compared to a one-tailed test.