Unpaired t-test
Find sample size:
If you can estimate group means and standard deviation, use this form to find the number of subjects you need.
Group 1 mean:
Group 2 mean:
or, enter difference between means:
Standard deviation:
Click here for sample size:
You will need subjects in Group 1
You will need subjects in Group 2
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.
N for Group 1:
Standard deviation:

Click here for effect size:
You can show a difference of size
For different power or significance level, change the fields below:
Alpha: Prob(reject H0 when H0 is true)
Power: Prob(reject H0 when H1 is true)
For unequal sample sizes, change the ratio below:
Choose another study design
v. 03/03
Contact: sfh2@columbia.edu
Source: G.W. Snedecor & W.G. Cochran
Statistical Methods (7th ed., p. 104)