Cohen's d Effect Size Calculator

The average of the first group. Only the difference between the two means matters, not their absolute size.

The standard deviation of group A. It is pooled with group B’s to form the denominator of d.

The number of observations in group A. It weights the pooled SD, converts a t statistic into d, and drives the Hedges’ g small-sample correction.

The average of the second group. d measures how far apart the two means are, in pooled-SD units.

The standard deviation of group B, pooled with group A’s when computing d.

The number of observations in group B. Used the same way as n for group A: pooling, the t conversion and the Hedges’ g correction.

The two-sample t statistic to convert, e.g. from a published paper. Together with the group sizes it gives d = t·√(1/n₁ + 1/n₂).