Evenness Index Calculator

Species evenness measures how uniformly individuals are distributed among the species present in a community. A perfectly even community has all species represented by the same number of individuals, while a low evenness value indicates that a few dominant species account for most individuals.

Pielou's J is calculated by dividing the observed Shannon diversity index (H) by the maximum possible diversity (ln S, where S is species richness). The result ranges from 0 to 1 — a value of 1 means perfect evenness, and values closer to 0 indicate increasing dominance by fewer species.

Pielou's J is popular because it is simple to calculate, standardised between 0 and 1, and directly comparable across communities with different species richness. It pairs naturally with the Shannon diversity index, which is itself one of the most widely adopted biodiversity metrics in ecological research.

There is no universal threshold, but values above 0.75 are generally considered high evenness, suggesting a well-balanced community. Values below 0.5 often indicate strong dominance by one or a few species. Context matters — some ecosystems naturally have uneven distributions.

The Shannon diversity index H = −Σ[pᵢ × ln(pᵢ)] quantifies both species richness and evenness in a single value. Pielou's J is derived from H by dividing it by ln(S), effectively isolating the evenness component by controlling for the number of species present.

Yes. Other evenness metrics exist, such as Simpson's Evenness (E₁/D) and the Camargo evenness index. However, Pielou's J based on the Shannon index is by far the most commonly used measure due to its mathematical clarity and ease of interpretation.

You need the count of individuals for each species in your sample — for example, from a field survey or experimental observation. Simply enter these counts as comma-separated numbers (e.g. 50, 30, 20, 10). The calculator will compute H, J, species richness, and provide a full species breakdown table.

Yes. Unlike Pielou's J, the Shannon index H is not bounded by 1. Its maximum value is ln(S), so for a community with 10 equally abundant species, H would be approximately 2.303. Pielou's J, however, is always between 0 and 1 because it divides H by this maximum.