|Find sample size:
If you can estimate group means and standard deviation, use this form to find the number of subjects you need.
|Find effect size:
If you know the number of subjects and the standard deviation of your measurement, use this form to see how small a difference you can detect.
Choose another study design
Source: G.W. Snedecor & W.G. Cochran
Statistical Methods (7th ed., p. 104)