Sample Size for Paired t-Test

Calculate how many paired measurements you need when comparing before/after or matched subjects. Provide the expected mean difference, standard deviation of differences, and the correlation between pairs to size your study with the desired power.

Use it for

• Before-after studies on the same subjects or matched pairs
• Clinical crossover trials or repeated measurements
• Settings where within-pair correlation improves precision

Parameters to set

• Expected mean difference and standard deviation of differences
• Alpha, target power, and sidedness of the test
• Correlation between paired observations