Effect Size Calculator - Free Cohen's d, r, and η² Calculator
Effect Size Calculator
Calculate various effect size measures including Cohen's d, Pearson's r, eta squared (η²), and more. Essential for understanding the magnitude of differences or relationships.
Cohen's d Calculator
Group 1
Group 2
For independent samples t-test with equal group sizes
How to use this calculator
📏 How to Use This Calculator
- Select the effect size measure you want to calculate
- Choose your input method (e.g., from means or test statistics)
- Enter your data in the appropriate fields
- Click calculate to get the effect size and interpretation
- Use the converter tab to transform between different effect size measures
📐 Effect Size Measures
Cohen's d
Standardized mean difference between two groups
d = (M₁ - M₂) / SD_pooled
- • Small: d = 0.2
- • Medium: d = 0.5
- • Large: d = 0.8
Correlation r
Strength of linear relationship between variables
- • Small: r = 0.10
- • Medium: r = 0.30
- • Large: r = 0.50
Eta Squared (η²)
Proportion of variance explained in ANOVA
η² = SS_between / SS_total
- • Small: η² = 0.01
- • Medium: η² = 0.06
- • Large: η² = 0.14
🌟 Interpretation Guidelines
| Effect Size | Small | Medium | Large |
|---|---|---|---|
| Cohen's d | 0.20 | 0.50 | 0.80 |
| Correlation r | 0.10 | 0.30 | 0.50 |
| η² (ANOVA) | 0.01 | 0.06 | 0.14 |
| Cohen's f | 0.10 | 0.25 | 0.40 |
💡 Important Considerations
- • Effect sizes are independent of sample size
- • Context matters - a "small" effect can be practically important
- • Report confidence intervals with effect sizes when possible
- • Consider using Hedges' g for small samples (n < 20)
- • Multiple effect size measures provide different perspectives
- • Domain-specific benchmarks may differ from Cohen's guidelines
⚠️ Common Mistakes to Avoid
- • Don't confuse statistical significance with effect size
- • Avoid over-interpreting small effects in large samples
- • Remember that correlation does not imply causation
- • Don't ignore negative effect sizes - report direction
- • Consider practical significance alongside statistical measures
About this calculator
Calculate effect sizes including Cohen's d, Pearson's r, eta squared, and more. Essential for research and meta-analysis.
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