Sample Size & Power Calculator (for Surveys & Experiments)

Plan your study with this free Sample Size & Power Calculator. It supports: survey proportions (margin of error + FPC), two-proportion A/B tests, one-mean, and two-means (independent) designs. Choose your goal (compute sample size or compute power) and get instant results — plus an optional power curve.

How to use

1. Select Problem (Survey Proportion, Two Proportions, One Mean, Two Means).
2. Select Goal: Sample Size or Power.
3. Fill in parameters (α, power, MDE/effect size, σ, p’s, etc.).
4. Click Calculate. Toggle the power curve if desired.

Examples

• Survey: 95% confidence, E=0.05, p unknown → p=0.5, n≈385; with N=50,000 → FPC n≈381.
• A/B (proportions): α=0.05 (two-tailed), power=0.8, p₁=0.10 vs p₂=0.12 → n/group ≈ 3,900.
• One mean: α=0.05 (two-tailed), power=0.8, σ=10, Δ=3 → n≈70.
• Two means: α=0.05 (two-tailed), power=0.8, σ₁=σ₂=10, Δ=3 → n/group ≈ 140.

Notes: Planning formulas use normal approximations (common in survey & experiment design). For small samples or strict accuracy use exact or t-based methods.