Effect Size Calculator

What It Does

This calculator evaluates the effect size between two means (i.e., Cohen's d; Cohen, 1988), which is the difference between means divided by standard deviation.

Between-subjects Studies

Enter the two means, plus SDs for each mean. To compute effect size using pooled or control condition SD, only enter one SD.

Within-subjects Studies

For within-subjects studies, one must correct for dependence among means in order to make direct comparisons to effect sizes from between-subjects studies. To do this, you also need to enter the correlation between the two means, so that Morris and DeShon's (2002) equation 8 can be applied.

download effect size calculator in excel format


Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd ed.). Hillsdale, NJ: Lawrence Earlbaum Associates.
description of book

Morris, S. B., & DeShon, R. P. (2002). Combining effect size estimates in meta-analysis with repeated measures and independent-groups designs. Psychological Methods, 7, 105-125.
download article : doi link to abstract


While every effort has been made to ensure that computations and claims are correct, no warranty is being provided. It is up to you to double check my calculations and read and evaluate the source articles.