Effect Size Calculator

Effect size measures the practical significance of results — not just statistical significance.

What this calculator does

Cohen's benchmarks: d=0.2 small, d=0.5 medium, d=0.8 large.

Frequently asked questions

What is a good effect size?

Cohen's d: 0.2=small, 0.5=medium, 0.8=large. Most real-world interventions: d=0.3–0.5.