T-Test Calculator (Two Samples)
Compare the means of two groups with Welch's t-test (or Student's pooled test) from raw data — t-statistic, degrees of freedom, p-value and mean difference.
How to use
- 1Paste the values for group A and group B.
- 2Choose Welch's test (unequal variances, recommended) or Student's pooled test.
How it's calculated
Welch: t = (x̄₁ − x̄₂) ÷ √(s₁²/n₁ + s₂²/n₂), df by the Welch–Satterthwaite equation. Student: pooled variance with df = n₁ + n₂ − 2.
Frequently asked questions
Welch or Student?
Welch's test doesn't assume equal variances and performs well even when they are equal, so many statisticians recommend it as the default.
What about paired data?
For before/after measurements on the same subjects, use a paired t-test: compute the differences and test whether their mean is zero.
How much data do I need?
The t-test is fairly robust, but very small samples (under ~10 per group) with skewed data can mislead.