Sample Size Calculator

Free for everyone, no login. Plan how many participants your study needs.

What are you planning?

Significance level (α)Statistical power (1 − β)

Expected effect size (Cohen's d)0.2 small · 0.5 medium · 0.8 large

Per group

Total sample

126

Participants per group (two groups).

Estimates use standard normal-approximation formulas (Cohen, 1988) and assume simple random sampling and a two-sided test. Add ~10–20% to allow for dropout. For complex designs, consult a statistician.