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Cohen’s d Effect Size Calculator
Compute the signed pooled-variance standardized mean difference from group summaries.
Group A sample count, Group A mean, Group A sample standard deviation, Group B sample count, Group B mean, Group B sample standard deviation
JSON
Browser only
Runs locally in your browser. Your files, pasted content and generated output are not uploaded. Reset clears this tool’s working data.
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How to use this tool
- Enter the labelled values and use the displayed units.
- Choose Calculate result and inspect the full report, assumptions and undefined/no-solution status.
- Choose Download result to save the complete JSON. Reset clears results and restores the example controls.
Examples
Group A sample count: 20
Group A mean: 10
Group A sample standard deviation: 2
Group B sample count: 30
Group B mean: 8
Group B sample standard deviation: 3
Limitations
- Independent group n>=2,finite means,nonnegative sample deviations; n<=1e9. Degree-of-freedom weighted pooled SD. Zero pooled SD gives null d with explicit undefined status. No paired design,Hedges correction,p-value or magnitude interpretation.
- Scalar numeric inputs use explicit decimal syntax and IEEE-754 arithmetic; unless a tighter bound is stated, positive values are 1e-12–1e12 and nonnegative values 0–1e12. Derived inventory counts above 1 billion and nonfinite results are refused. Combined input limit400,000 UTF-8 bytes;complete JSON output limit4MiB. Numeric/code input controls allow128 characters. All processing stays in your browser.
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