Simpson's Diversity Index
Calculate Simpson's index (D), the Gini-Simpson index (1 − D), the inverse Simpson index and evenness from species counts, free online.
About this calculator
Simpson's D = Σ n(n−1) ÷ N(N−1) is the probability that two individuals drawn at random are the same species. 1 − D is the probability they differ (higher means more diverse) and 1/D is the effective number of equally common species.