Sample Size & Power Calculator
Free biostatistics calculator for clinical trials, bioassays, and regulated research. No sign-up required.
for a proportion with 95% confidence and ±5.0% margin of error
Why this exists
Biotech teams run sample-size and power calculations every week. We built this free calculator so you can check your numbers instantly — and so you can see what Quandra v8 automates behind the scenes.
- Deterministic formulas, no black box
- Built for proportions, means, and two-group power
- No email or account required
Method notes
Uses normal-approximation formulas suitable for planning and quick checks. For final regulatory submissions, pair this with a statistician-reviewed SAP and validated software.
How to use this calculator
Sample size for proportions
Use this when your endpoint is a percentage — response rates, pass/fail rates, or adverse-event proportions. Enter your expected proportion and the margin of error you can tolerate.
Sample size for means
Use this for continuous endpoints like concentration, potency, or cell viability. You need an estimate of standard deviation and the precision you want around the mean.
Two-group power analysis
Use this to compare two arms — treatment vs. control, new assay vs. reference method. Enter the smallest clinically relevant difference, the standard deviation, and your desired power.
Margin of error
Already collected data? Enter your sample size and observed proportion to see the confidence interval width. Useful for reporting and QC.
What Quandra v8 adds
This calculator gives you one number at a time. Quandra v8 writes the full statistical analysis plan, generates R/SAS code, cross-checks assumptions, and keeps an audit trail for regulated work.