How to use this calculator
An effect size expresses the difference between two group means relative to within-group variation. This calculator uses the conventional pooled sample standard deviation for independent groups and preserves the sign of group 1 minus group 2. An approximate small-sample Hedges correction is provided as a separate metric.
The method
Enter the values in the labeled fields, check the units or selected mode, and choose Calculate. The result includes the applicable working and a breakdown or visual when useful. Change an input and calculate again to update the result.
Group 1 mean: 80 Group 1 sample SD: 10 Group 1 sample size: 30 Group 2 mean: 75 Group 2 sample SD: 12 Group 2 sample size: 30
Cohen's d: 0.4526787302
Signed standardized difference: group 1 minus group 2.
Scope and limitations
Independent-group summary data only. Each sample size must be at least 2, and the pooled standard deviation must be positive. No paired-sample adjustment, confidence interval, power estimate, or significance test is performed.
Common questions
What does a negative d mean?
The mean of group 1 is lower than the mean of group 2 under the chosen group order.
Does a large d prove statistical significance?
No. Effect size and statistical significance answer different questions. Interpretation also depends on context and study design.
References & further reading
External references provide background, not an endorsement of this implementation. See our methodology for numerical conventions and limitations.