# Simpson Diversity Index (D = 1 − Σpᵢ²) Compute Gini–Simpson D, dominance λ, reciprocal 1/λ, and Simpson evenness from species counts. > Canonical page: https://elysiatools.com/en/tools/simpson-diversity-index - **Category:** Health - **Keywords:** simpson diversity index, gini simpson, simpson dominance, species diversity, hill number, effective species number, reciprocal index, evenness, biodiversity, ecology calculator, community structure, lab calculator ## Overview Enter species abundance counts (one per line, or separated by commas or spaces) to compute Simpson-family diversity metrics. The calculator returns Gini–Simpson D = 1 − Σpᵢ², dominance λ = Σpᵢ², the reciprocal 1/λ (effective species number), and Simpson evenness from the observed richness and total N. ## Inputs - **Species counts (one per line)** (textarea): One abundance count per species, separated by new lines, commas, or spaces. ## When to use - You have raw species counts from a plot, transect, or lab sample and need D, λ, 1/λ, and evenness in one step. - You want the probability that two random individuals belong to different species, plus the equivalent number of equally common taxa. - You need to compare community structure when literature uses different Simpson conventions (λ, 1 − λ, or 1/λ). ## How it works - Paste positive abundance counts for each species; zeros and empty lines are ignored. At least two species with positive counts are required. - The tool converts counts to proportions pᵢ, then computes λ = Σpᵢ², Gini–Simpson D = 1 − λ, the reciprocal 1/λ, and evenness (1/λ)/S. - Results include richness S, total N, the proportion vector, and a short interpretation of dominance versus evenness. - All four Simpson-family values are reported so you can match the definition used in your field. ## Use cases - Summarize plot or quadrat counts into Gini–Simpson D and effective species number for biodiversity reports. - Check whether a community is dominated (high λ, low 1/λ) or relatively even before comparing sites. - Convert lab or field species tallies into λ, D, 1/λ, and evenness for ecology coursework or papers. ## Frequently asked questions ### What counts can I enter? One non-negative abundance per species, separated by new lines, commas, or spaces. Only positive counts contribute to richness and the indices. ### What is Gini–Simpson D? D = 1 − Σpᵢ² is the probability that two randomly drawn individuals belong to different species. It ranges from 0 (complete dominance) toward 1 (high diversity). ### How is the reciprocal 1/λ interpreted? 1/λ is the Hill number of order 2: the number of equally common species that would produce the same λ. It is easier to compare across communities than D. ### What is Simpson evenness? Evenness is (1/λ)/S. Values near 1 mean abundances are similar; lower values indicate a few taxa dominate. ### Why do some papers call λ the Simpson index? Literature uses λ, 1 − λ, or 1/λ interchangeably. This tool reports all three so you can match the convention in your source. ## Related tools - [Extended BMR Calculator (Mifflin / Schofield Multi-Formula Comparison)](https://elysiatools.com/en/tools/basal-metabolic-rate-ext): Compare Mifflin-St Jeor, original and revised Harris-Benedict, Schofield (FAO/WHO/UNU), and Katch-McArdle BMR equations side by side with mean and spread in kcal/day. 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