Cohen d and Hedges g Calculator
Compare independent-group Cohen d, gamma-corrected Hedges g and Glass delta from sample summary statistics.
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Result
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Calculation steps
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How to calculate
Pool sample variances with their n−1 weights and standardize the first-minus-second mean difference, applying the exact gamma-ratio Hedges correction.
d=(mean1−mean2)/pooled SD; g=J(df)×d; Glass delta=(mean1−mean2)/SD2
Worked example
Means 12 and 10 with both sample SDs 2 give pooled Cohen d=1. With 20 observations per group, the finite-sample Hedges correction makes g slightly smaller than 1.
Assumptions and input details
Independent groups with sample sizes at least two. Pooled SD must be positive; Glass delta is undefined when the chosen group-2 reference SD is zero. These are descriptive standardized mean differences, not paired d variants, causal effects or universal importance categories. No confidence interval or power calculation is supplied.
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
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The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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