Mean · MEAN-CI
Sample Size for Estimation of a Mean
Plan the sample size needed to estimate one population mean with a chosen confidence level and absolute margin of error.
3. Results
Enter the planning assumptions and select Calculate.
Suggested sample-size wording
Warnings
Formula, assumptions, limitations, and methodological note
Example clinical scenario
A community survey aims to estimate mean systolic blood pressure among adults with a prespecified confidence level and margin of error.
Formula and methodological note
The calculator uses the normal-approximation precision formula: n = (z × SD / d)², where z is the two-sided confidence-level quantile, SD is the planning standard deviation, and d is the absolute margin of error. The unadjusted sample size is rounded up before the dropout/non-response adjustment is applied.
It is intended for estimating one continuous, approximately normally distributed population mean using independent observations. The planning SD should come from a relevant prior study, pilot study, or other defensible source and use the same outcome units as the margin of error.
It does not account for finite-population correction, clustering, design effects, stratification, weighting, repeated measurements, or markedly non-normal outcomes. Consider the dedicated finite-population-correction calculator when the eligible population is small.
Technical results
Method references
- Cochran WG. Sampling Techniques. 3rd ed. John Wiley & Sons; 1977.
- Chow SC, Shao J, Wang H, Lokhnygina Y. Sample Size Calculations in Clinical Research. 3rd ed. Chapman and Hall/CRC; 2017.
Suggested citation
Yaacob, Najib Majdi. “Sample Size for Estimation of a Mean (MEAN-CI).” Web calculator. NajibMY, 2026. Accessed July 29, 2026. https://najibmy.netlify.app/tools/sample-size/mean/estimate-mean/.