Two Sample T-Test Calculator
Compare two independent groups with Welch's t-test.
Enter your values
ⓘ Live results
Results
- t statistic
- -5.5549
- p-value (two-tailed)
- 0.0002
- Verdict
- p < 0.001 — very strong evidence
- Group means
- 24.5 vs 30.5
- Difference
- -6
- Welch degrees of freedom
- 10
- Cohen's d
- -3.207
Quick answer
Welch's t-test compares two independent means without assuming equal variances: t = (x̄₁ − x̄₂) ÷ √(s₁²/n₁ + s₂²/n₂).
t = (x̄₁ − x̄₂) ÷ √(s₁²/n₁ + s₂²/n₂)
How to use the Two Sample T-Test Calculator
- 1Enter every value from group 1.
- 2Enter every value from group 2 — the groups can be different sizes.
- 3Read t and p, then use Cohen's d to judge whether the gap matters in practice.
Worked example
Using the values the calculator loads with:
Inputs
- Group 1 values22, 25, 27, 24, 23, 26
- Group 2 values28, 31, 29, 33, 30, 32
Results
- t statistic-5.5549
- p-value (two-tailed)0.0002
- Verdictp < 0.001 — very strong evidence
- Group means24.5 vs 30.5
- Difference-6
- Welch degrees of freedom10
- Cohen's d-3.207
Frequently asked questions
Why Welch instead of Student's t-test?
Welch's version does not assume the two groups share a variance, and it performs at least as well when they do. Most statisticians now use it by default.
What counts as a large effect?
Cohen's rough guide: 0.2 small, 0.5 medium, 0.8 large — but context beats the rule of thumb.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.