Sample Size and Power Calculator
Use the advanced sample size calculator to size studies for estimation or hypothesis testing. Switch between confidence-interval planning and power calculations in one place, whether you need to estimate a mean, a proportion, or compare groups with t-tests and rate tests.
- Sample size for mean estimates
- Sample size for proportions
- Sample size for rates
- Two-sample t-test sample size
- One-sample t-test sample size
- Paired t-test sample size
- One-sample proportion test sample size
- Two-sample proportion test sample size
- One-sample Poisson test sample size
- Two-sample Poisson test sample size
Why plan sample size up front?
A clear sample size plan protects your study from being underpowered or too costly. The calculator keeps alpha, power, effect sizes, allocation ratios, and exposure in sync, so you can defend your design with transparent assumptions.