Sample Size Calculators

for designing clinical research

Sample Size Calculators

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If you are a clinical researcher trying to determine how many subjects to include in your study or you have another question related to sample size or power calculations, we developed this website for you. Our approach is based on Chapters 5 and 6 in the 4th edition of Designing Clinical Research (DCR-4), but the material and calculators provided here go well beyond an introductory textbook on clinical research methods.

This project was supported by the National Center for Advancing Translational Sciences, National Institutes of Health, through UCSF-CTSI Grant Numbers UL1 TR000004 and UL1 TR001872. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIH.


Please cite this site wherever used in published work:

Kohn MA, Senyak J. Sample Size Calculators [website]. UCSF CTSI. 28 September 2024. Available at https://www.sample-size.net/ [Accessed 20 November 2024]


Software utilities developed by Michael Kohn. Programming and site development by Josh Senyak at Quicksilver Consulting. Thanks to Mike Jarrett at quesgen.com for an early version of this site. Graphic design by Emanuel Heim Design.


This site was last updated on September 28, 2024.