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Hedges G Calculator

Calculate Hedges’ g, the small-sample corrected standardised mean difference.

About Hedges G Calculator

The correction is roughly 5 per cent at a total sample of 20 and under 1 per cent above 100. It is always downward, since Cohen’s d overestimates the population effect in small samples. Meta-analyses use Hedges’ g rather than Cohen’s d precisely because they combine studies with very different sample sizes.

Formula

Hedges G

g = d × (1 − 3 ÷ (4N − 9))

correction factor
Approaches 1 as total sample size grows

Worked example

With the default values below, Hedges G Calculator returns Hedges’ g of 0.53458. Change any input above and every figure here is recalculated in your browser.

Inputs used

Cohen’s d
0.55
Sample size of group 1minimum 2
15
Sample size of group 2minimum 2
14

Results

Hedges’ g
0.53458
Correction Factor
0.971963
Upward Bias Removed
2.8037%
Total Sample Size
29
Magnitude
Medium

Step by step

  1. 1Values used
  2. 2Hedges G
  3. 3Hedges’ g= 0.53458
  4. 4Correction Factor= 0.971963
  5. 5Upward Bias Removed= 2.8037
  6. 6Total Sample Size= 29
  7. 7Magnitude= Medium

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Hedges G calculated?

g = d × (1 − 3 ÷ (4N − 9)) The correction is roughly 5 per cent at a total sample of 20 and under 1 per cent above 100. It is always downward, since Cohen’s d overestimates the population effect in small samples.

Why does Hedges G matter?

Meta-analyses use Hedges’ g rather than Cohen’s d precisely because they combine studies with very different sample sizes.

What values do I need to enter?

This calculator takes 3 inputs: Cohen’s d, Sample size of group 1, Sample size of group 2. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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