Chi-Square Test Calculator
Goodness-of-fit test from observed and expected counts.
Enter your values
Enter the observed counts you are working with.
Enter the expected counts you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Chi-square
- 38.1818
- p-value
- < 0.0001
- Verdict
- p < 0.001 — very strong evidence
- Degrees of freedom
- 5
- Biggest contributor
- Category 5 (17.45)
- Cramér's V
- 0.195
Quick answer
Chi-square sums (observed − expected)² ÷ expected across categories; large values mean the observed pattern is unlikely under the expected model.
χ² = Σ (O − E)² ÷ E
At a glance
| What it does | Goodness-of-fit test from observed and expected counts. |
|---|---|
| Category | Statistics |
| Inputs needed | Observed counts, Expected counts |
| Main output | Chi-square |
| Formula | χ² = Σ (O − E)² ÷ E |
| Cost | Free — no sign-up, no download |
How to use the Chi-Square Test Calculator
- 1Enter the counts you actually observed, in category order.
- 2Enter the counts the null hypothesis expects — equal shares if you have no other model.
- 3Check the p-value, then look at which category contributed most to the total.
Inputs explained
- Observed counts
- Enter the observed counts you are working with.
- Expected counts
- Enter the expected counts you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- Observed counts30, 14, 34, 45, 57, 20
- Expected counts33, 33, 33, 33, 33, 33
Results
- Chi-square38.1818
- p-value< 0.0001
- Verdictp < 0.001 — very strong evidence
- Degrees of freedom5
- Biggest contributorCategory 5 (17.45)
- Cramér's V0.195
Frequently asked questions
What if an expected count is below 5?
The chi-square approximation gets unreliable. Combine small categories or use Fisher's exact test.
Can I use percentages?
No. Chi-square must run on raw counts; percentages throw away the sample size the test depends on.
What do I need to enter into the Chi-Square Test Calculator?
Just 2 values: observed counts, expected counts. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Chi-Square Test Calculator work out the answer?
Chi-square sums (observed − expected)² ÷ expected across categories; large values mean the observed pattern is unlikely under the expected model. It applies the formula χ² = Σ (O − E)² ÷ E and shows the working so you can check each step by hand.
Is the Chi-Square Test Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.