How to use the statistical power calculator
Estimate power of a two-sample comparison. Enter effect size d, per-group sample size, significance level α in the fields above; the power is computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- d — Effect size d
- n — Per-group sample size
- a — Significance level α
Worked example
With effect size d = 0.5, per-group sample size = 64, significance level α = 0.05, the calculator gives power ≈ 0.8074296.
Frequently asked questions
What is the formula for the statistical power calculation?
Power = ncdf(d × √(n / 2)-norminv(1-a / 2)). Here d is effect size d, n is per-group sample size, a is significance level α.
What inputs do I need for the statistical power calculator (two means) calculator?
You need effect size d, per-group sample size, significance level α. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.