Calculators based on Chapters 5 and 6 of Designing Clinical Research (5th Edition) are available on the UCSF CTSI Sample Size website, created by Michael Kohn.

To help you figure out which sample size calculator to use, you can start with the Calculator finder.

Here are some commonly used sample size calculators (all links will take you off the DCR-5 website) to a samplesize.net calculator:

• Means – effect size    Use this link if you already know your sample sizes in each group, and want to know how small a difference in means you can detect at a given power and alpha.
• Proportions- effect size  Use this link if you already know your sample sizes in each group, and want to know how small a difference in proportions you can detect at a given power and alpha.
• Means – sample size  Use this link if you want to estimate how many subjects you’ll need to detect a given difference in means.  (You’ll need the standard deviation of the variable.)
• Proportions – sample size  Use this link if you want to estimate how many subjects you’ll need to detect a difference between two proportions.