Shannon Diversity Index Calculator

Calculate the Shannon diversity index (H) and evenness from species counts.

Enter the number of individuals for each species, separated by commas, spaces, or new lines. Zeros and blank entries are ignored.

What the Shannon Diversity Index Measures

The Shannon diversity index (also called the Shannon-Wiener or Shannon-Weaver index, H') quantifies the biodiversity of a community by combining two components: species richness (how many different species are present) and evenness (how equally the individuals are distributed among those species).

For each species, the proportion of individuals is páµ¢ = náµ¢ / N, where náµ¢ is the count for species i and N is the total number of individuals. The index is calculated as:

H' = −Σ (pᵢ × ln pᵢ)

A higher value indicates greater diversity. The index increases both when more species are added and when individuals are spread more evenly across species. By convention, the natural logarithm (ln) is used here, so H' is reported in nats.

How to Interpret the Value

Shannon index values typically fall between 1.5 and 3.5 for most ecological communities, and rarely exceed 4.5. The exact range depends on the number of species sampled:

  • H' below 1.5: low diversity — few species and/or strong dominance by one or two species.
  • H' between 1.5 and 2.5: moderate diversity, common in many natural habitats.
  • H' between 2.5 and 3.5: high diversity with many species fairly evenly represented.
  • H' above 3.5: very high diversity, usually requiring a large, even species pool.

The maximum possible value for a given sample is ln(S), achieved only when every species has exactly the same number of individuals.

Pielou's Evenness

Pielou's evenness (E) standardizes the Shannon index against its maximum possible value, isolating the evenness component from richness:

E = H' / ln(S)

Evenness ranges from 0 to 1. A value near 1 means all species are present in roughly equal abundance, while a value near 0 means the community is dominated by one or a few species. For example, the counts [10, 10, 10, 10] give H' = ln(4) ≈ 1.386 and a perfect evenness of 1. Evenness is undefined when there is only a single species (S = 1), since ln(1) = 0.

References

  • Shannon, C. E. (1948). A Mathematical Theory of Communication. Bell System Technical Journal.
  • Pielou, E. C. (1966). The measurement of diversity in different types of biological collections. Journal of Theoretical Biology.
  • Magurran, A. E. (2004). Measuring Biological Diversity. Blackwell Publishing.

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Educational Disclaimer: This Shannon diversity index calculator is provided for educational purposes. Diversity indices are sensitive to sampling effort and methodology; results should be interpreted in the context of how the data were collected. For research or conservation decisions, consult a qualified ecologist.

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