Sample Size for Two-Sample t-Test

Size your study for comparing two independent means. Choose whether you work with a raw mean difference or a standardized effect size (Cohen's d), set alpha, power, and the allocation ratio, and get the group sizes you need.

Use this when

• You compare treatment vs. control groups with independent subjects
• You want to account for equal or unequal variances across the two groups
• Power needs to reflect the exact alpha and sidedness of your test

What to enter

• Effect size (difference or Cohen's d)
• Standard deviations or pooled standard deviation
• Alpha level, power target, and allocation ratio