What this calculator does
Simpson’s diversity index is an ecology and biodiversity metric that measures how varied a community is, taking into account both the number of different species (or categories) present and how evenly individuals are distributed among them.
How the calculation works
Simpson’s Index (D) estimates the probability that two individuals picked at random from the community belong to the same species: D = Σnᵢ(nᵢ-1) / N(N-1), where nᵢ is the count in each category and N is the total count. Because a higher D means lower diversity, the calculator reports Simpson’s Diversity Index as 1 – D, which increases with diversity and ranges from 0 (no diversity) to just under 1 (very high diversity). The reciprocal index (1/D) is another common way to express the same idea as an effective number of equally common species.
Enter at least 2 categories with a combined total of more than 1 individual. This tool is for general ecological and educational use.