Compute Cohen’s d and Hedges’ g from two group means, standard deviations and sample sizes, with interpretation.
Result
How to use this tool
Enter group 1 and group 2 means.
Enter each group’s standard deviation and n.
Read Cohen’s d and the corrected Hedges’ g.
Use the size label as a rough guide, not a verdict.
Formula & worked example
Means 105 and 100 with SD 10 in both groups (n = 30 each) give Cohen’s d = 0.5 and Hedges’ g = 0.4935, a medium effect.
Limitations — read this before you rely on it
Assumes roughly normal data and similar variances; it is a descriptive effect size, not a significance test.
Frequently asked questions
The difference between two means divided by the pooled standard deviation, so effects are comparable across scales.
For small samples, where g corrects the slight upward bias in d.
By Cohen’s rough conventions, yes, but what counts as important depends on the field and the outcome.
No: it measures size, not whether the result could be chance; report it with a confidence interval or p-value.
The pooled SD assumes similar spread; with very unequal SDs, consider Glass’s delta or a Welch-style variant.