Two Sample T-Test Calculator
Compare two independent groups with Welch's t-test.
Enter your values
Enter the group 1 values you are working with.
Enter the group 2 values 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.
- 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)
At a glance
| What it does | Compare two independent groups with Welch's t-test. |
|---|---|
| Category | Statistics |
| Inputs needed | Group 1 values, Group 2 values |
| Main output | t statistic |
| Formula | t = (x̄₁ − x̄₂) ÷ √(s₁²/n₁ + s₂²/n₂) |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Group 1 values
- Enter the group 1 values you are working with.
- Group 2 values
- Enter the group 2 values you are working with.
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.
What do I need to enter into the Two Sample T-Test Calculator?
Just 2 values: group 1 values, group 2 values. 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 Two Sample T-Test Calculator work out the answer?
Welch's t-test compares two independent means without assuming equal variances: t = (x̄₁ − x̄₂) ÷ √(s₁²/n₁ + s₂²/n₂). It applies the formula t = (x̄₁ − x̄₂) ÷ √(s₁²/n₁ + s₂²/n₂) and shows the working so you can check each step by hand.
Is the Two Sample T-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.