About Scientific Sample Size Calculator (Cochran & FPC)
Publication-standard sample size determination tool for clinical trials, surveys, and scientific studies. Uses Cochran’s formula for infinite populations and applies Finite Population Correction (FPC) for known population sizes. Includes an interactive sensitivity matrix across varying margins of error.
Key Capabilities & Features
- Cochran’s foundational formula with critical values Z* for 80%, 90%, 95%, 98%, 99%, and 99.9% confidence
- Finite Population Correction (FPC) preventing oversampling in finite or bounded populations
- Adjustable margin of error (±0.1% to ±20%) and expected population proportion (default 0.50)
- Sensitivity comparison matrix displaying required sample sizes across 7 margin-of-error benchmarks
- Instant real-time recalibration as population size or confidence parameters change
How to Use Scientific Sample Size Calculator (Cochran & FPC)
Select Confidence Level
Choose your desired confidence level (95% is standard for academic studies).
Set Target Margin of Error
Adjust the slider for acceptable precision (e.g. ±5% or ±3%).
Specify Population Size (Optional)
Enter total population N if known, or leave blank for large/infinite populations.
Review Required Sample Size
Read the minimum participant sample required and inspect the sensitivity matrix.
Privacy & In-Browser Execution Guarantee
100% Client-Side. Study design parameters and population inputs remain strictly private on your device.
Frequently Asked Questions
Why does expected proportion p = 0.5 produce the largest sample size?
The variance of a proportion p(1 - p) reaches its mathematical maximum at p = 0.5, ensuring your sample size is sufficiently powered even if true prevalence is unknown.
When is Finite Population Correction (FPC) necessary?
FPC is recommended whenever the initial sample size exceeds 5% of the total target population size (n/N > 0.05).