How to use Effect Size Calculator
- Choose two-group difference or correlation association.
- Enter sample counts, means and sample standard deviations, or r.
- Review the formula, direction and limitations.
Example: Effect Size Calculator
Effect Size Calculator: Cohen's d = 0.666666666667; approximate Hedges g = 0.653421633554.
Options
- Independent groups
- Enter each sample size, mean and sample standard deviation. The difference is group 1 minus group 2.
- Association mode
- Squaring a supplied Pearson r removes its sign. It does not establish causality or a clinical interpretation.
Supported inputs and limits
Where your input is processed
This tool processes your input in this browser. Your text and files are not uploaded to UseFreeTools. Check this tool's limits for anything it may save on your device.
A standardized difference needs its model stated
The group calculation uses a pooled sample standard deviation and an approximate Hedges correction. It is for independent groups, not paired observations. Keep group order and the reported method with the number; the page does not add uncertainty intervals or judge whether a difference is practically meaningful.
Questions about Effect Size Calculator
What determines the sign of d?
Group one mean minus group two mean. Swapping the groups reverses the sign.
Is the Hedges correction exact?
No. It uses J = 1 - 3/(4df - 1), labeled as an approximation.
Does a larger effect prove causation?
No. An effect size describes these supplied summaries; study design, uncertainty and confounding remain separate.