Sample Size & Power

Sample Size & Power is a fast, fully offline study-planning tool. Pick the effect size you'd care about, your false-alarm rate, and the power you want - it tells you exactly how many subjects you need, then shows the power you'd get at any sample size.

Too few subjects and a real effect slips by unnoticed. Too many wastes time and money. Power analysis finds the sweet spot before you collect a single data point.

WHAT'S INSIDE

Plan
Set the effect size, alpha, target power, and one/two-sample or one/two-tailed - get the required n, total subjects, and the power at your own sample size instantly.

Power
The power curve (power vs n, with your target line and required-n marker), the null-vs-real overlap diagram, and the sample-size-vs-effect-size trade-off.

Idea
A plain-English walkthrough of why studies need enough subjects - effect size, alpha, power, and the two kinds of errors - with formulas rendered in offline KaTeX.

Sim
Drag effect size and n and watch the curves pull apart and the power change live. Send your settings straight to the Plan tab.

Cases
Worked study-planning examples - a drug trial, a teaching method, a before-and-after design - that load with one tap.

WHY SAMPLE SIZE & POWER

- 100% offline - your data never leaves your device
- No account, no sign-up, no clutter
- A distinctive gauge/speedometer-needle navigation, built just for this app
- Required n, achieved power, and the full trade-off - not just one number
- Input is never lost - your design is saved automatically

Whether you're a student learning why power analysis matters, a researcher planning a real study, or just curious how many subjects an experiment actually needs, Sample Size & Power gives you the answer before you start collecting data.