Effect Size Calculator

Need to work with effect sizes?

Convert between different effect size measures, work out the effect size from a test statistic (whether from a published paper or your own analysis output), or calculate one from group means and standard deviations. Free, instant, and ready to use in your research.

Three ways this tool can help
1

Convert

You have an effect size in one form (for example, d) and need it in another (for example, r or η²).

2

Extract

Your analysis output or a published paper gives a test statistic (like t, F, or χ²) and you need to work out the effect size from it.

3

Calculate

You have the means and standard deviations from two groups and want to know how big the difference is.

What is an effect size?

An effect size is a number that tells you how big a difference, relationship, or change is — not just whether it exists. A p-value tells you if something is statistically significant; an effect size tells you if it actually matters in practice.
Why are there so many types?
Different statistical tests use different effect size measures. A t-test uses Cohen’s d, correlations use r, ANOVA uses η² or Cohen’s f, and so on. This tool lets you move between them.
How are they interpreted?
Cohen (1988) proposed general benchmarks: small (a subtle effect that is hard to see), medium (noticeable and meaningful), and large (obvious and strong). These are guidelines, not rules — always consider what is meaningful in your own research area.

What would you like to do?

Choose the option that best describes your situation.

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Convert between effect size measures

You already have an effect size and need to express it in a different form.

Example: you have d = 0.50 and need to know the equivalent r or η²
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Extract from a test statistic

Your software gave you a test result, or a published paper reports one, and you need to work out the effect size.

Example: your SPSS output or a paper reports t(58) = 2.45 and you need to find d
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Calculate from group data

You have means and standard deviations from two groups and want to know the effect size.

Example: Group 1: M = 25.3, SD = 5.1; Group 2: M = 22.8, SD = 4.9