Simpson Diversity Index Calculator

Work out simpson diversity index instantly with clear inputs, formula shown and shareable results.

About Simpson Diversity Index Calculator

Sums the squared proportional abundances to give Simpson's dominance, then reports both the Gini-Simpson and reciprocal forms.

Formula

Simpson's index

D = sum(pi^2); Gini-Simpson = 1 - D; reciprocal Simpson = 1/D, which equals the effective number of dominant species

Worked example

With the default values below, Simpson Diversity Index Calculator returns Selected Simpson index of 0.7000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Individuals per species: 40, 30, 20, 10
Index formone of 1 - D (Gini-Simpson), 1/D (reciprocal): 1 - D (Gini-Simpson)

Results

Selected Simpson index: 0.7000
Simpson's dominance (D): 0.3000
Gini-Simpson index (1 - D): 0.7000
Reciprocal Simpson (1/D): 3.3333

Step by step

1Values used
2Simpson's index
3Selected Simpson index= 0.7000
4Simpson's dominance (D)= 0.3000
5Gini-Simpson index (1 - D)= 0.7000
6Reciprocal Simpson (1/D)= 3.3333

Assumptions and limits

The result is derived only from the 2 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 4 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 does Simpson differ from Shannon?

Simpson weights the commonest species more heavily, so it is less sensitive to rare species than Shannon.

What does 1 - D mean intuitively?

The probability that two individuals drawn at random belong to different species.