BIOMEDICAL STATISTICS-SIMPLIFIED

Sample Size

Sample size calculator for common study designs.

Choose the design, enter the anticipated parameters, and the page will estimate the required total sample size. These formulas are meant for common planning scenarios, not complex adaptive, clustered, or multilevel designs.

Study design

Pick the sample size scenario closest to your planned study.

Single proportion / prevalence study

Estimate a prevalence or proportion with a desired margin of error.

Confidence levelMargin of error / precision

Expected prevalence or proportion

Enter proportions as decimals such as `0.20` for 20%.

Result

Estimated sample size under the selected assumptions.

Choose a study design, enter assumptions, and calculate to view the estimated sample size.

Formula References

Vancouver-style references for the simplified formulas used on this page.

Lwanga SK, Lemeshow S. Sample size determination in health studies: a practical manual. Geneva: World Health Organization; 1991. Available from: https://iris.who.int/handle/10665/40062
Charan J, Biswas T. How to calculate sample size for different study designs in medical research? Indian J Psychol Med. 2013;35(2):121-6. Available from: https://journals.sagepub.com/doi/pdf/10.4103/0253-7176.116232
Buderer NM. Statistical methodology: I. Incorporating the prevalence of disease into the sample size calculation for sensitivity and specificity. Acad Emerg Med. 1996;3(9):895-900. doi:10.1111/j.1553-2712.1996.tb03538.x. Available from: https://pubmed.ncbi.nlm.nih.gov/8870764/

These are simplified planning formulas for common situations. For matched studies, cluster sampling, unequal allocation, time-to-event outcomes, repeated measures, or multivariable model development, a biostatistician should review the planned design.