Shannon Diversity Index Calculator
Enter species counts from a community sample to compute the Shannon diversity index (H'), a standard measure combining species richness and evenness into a single diversity score. Two 3D diagrams compare a low-diversity and high-diversity community, and charts show how evenness and richness each affect the final index.
Reviewed by the ToolNestr Editorial Team — July 2026
Enter the count of individuals for each species (up to 4 species, leave unused fields blank).
Low vs high diversity communities
1. Low diversity (one species dominates)
Mostly one color (species) with only a few individuals of others — low H'.
2. High diversity (evenly distributed)
Multiple species (colors) represented in roughly equal numbers — high H'.
Shannon diversity graphs
How it works
The core idea in one line: the Shannon index measures how unpredictable a randomly picked individual's species identity is — a community where one species dominates is very predictable (low diversity), while one where species are evenly and richly represented is highly unpredictable (high diversity).
H' = −Σ(pᵢ × ln(pᵢ))
pᵢ = proportion of individuals belonging to species i
E = H' / ln(S)
evenness — S = total number of species, ranges from 0 to 1
Borrowed directly from Claude Shannon's information theory, the formula H'=−Σ(pᵢ ln pᵢ) treats each species' proportion pᵢ as a probability, and −ln(pᵢ) as the 'surprise' of encountering that species — rare species carry more surprise, common ones less. Weighting each species' surprise by its own proportion and summing across all species produces a single number that rewards both having many species (richness) and having them represented in balanced proportions (evenness), which is exactly why two communities with the same species count can still have very different H' values.
Worked example 1 — a community with 3 species
Given: A sample contains 40 individuals of species A, 30 of species B, and 30 of species C (100 total).
The relatively even distribution (40:30:30) across 3 species produces a fairly high H' close to the theoretical maximum for 3 species (ln(3)≈1.099).
Worked example 2 — computing evenness for the same community
Given: Using H' ≈ 1.089 from Example 1, with S = 3 species.
An evenness this close to 1 confirms the community is very evenly distributed among its 3 species — no single species dominates the sample.
How species distribution affects H' (fixed 3 species, 100 individuals)
The same 3 species and total count can produce very different diversity scores depending on how evenly individuals are distributed.
| Distribution | H' | Evenness |
|---|---|---|
| 98, 1, 1 (one species dominates) | 0.11 | 0.10 |
| 60, 20, 20 | 0.95 | 0.87 |
| 40, 30, 30 ★ | 1.09 | 0.99 |
| 34, 33, 33 (near-perfect evenness) | 1.10 | 1.00 |
★ Reference row (worked examples 1 & 2). Notice how dramatically H' and evenness both drop when one species dominates — richness alone (3 species in every row) doesn't capture this at all.
Where the Shannon diversity index actually matters
🌳 Forest and habitat biodiversity assessment
Ecologists use the Shannon index to quantify and compare biodiversity across different habitats, tracking changes over time or evaluating the impact of conservation and restoration efforts.
🌊 Water quality bioindicator studies
Aquatic ecologists use diversity indices of indicator species (like macroinvertebrates) to assess water quality — polluted waters typically show low diversity, dominated by a few pollution-tolerant species.
🌾 Agricultural and land-use impact studies
Comparing Shannon diversity before and after land-use changes (like converting forest to farmland) helps quantify biodiversity loss and informs sustainable land management policy.
🦠 Microbiome diversity research
Microbiologists apply the Shannon index to characterize the diversity of bacterial communities in the gut microbiome, soil samples, or other environments, linking diversity patterns to health and ecosystem function.
Common misconceptions
"Counting the number of species present is enough to measure diversity."
Simple species counts (richness) ignore how evenly individuals are distributed — a community dominated by one species with a few rare others feels much less diverse than one with the same species count evenly distributed, and only H' (not richness alone) captures that difference.
"A higher Shannon index always means a healthier ecosystem."
While diversity is often associated with ecosystem health and resilience, H' alone doesn't capture every aspect of ecosystem function — some naturally low-diversity ecosystems (like certain extreme environments) are perfectly healthy and stable for their context.
"H' has a fixed maximum value of 1, like a percentage."
H' has no fixed universal maximum — its ceiling depends on how many species are present (the theoretical maximum for S species is ln(S)). It's evenness (E), not H' itself, that is bounded between 0 and 1.
"Two communities with the same H' value must have identical species distributions."
Very different species distributions and even different numbers of species can produce similar H' values — this is a known limitation of the index, which is why ecologists often report richness and evenness separately for full context.
Formula sources & further reading
The formulas here are standard, traceable to:
- • OpenStax, Biology 2e — Chapter 19, "Population and Community Ecology" (free, peer-reviewed). openstax.org
- • Shannon, C.E. (1948) — "A Mathematical Theory of Communication," Bell System Technical Journal (original information-theory source of the formula).
- • Molles, Ecology: Concepts and Applications — Chapter 17, Species Abundance and Diversity.
H' = −Σ(pᵢ ln pᵢ); E = H'/ln(S). Originally derived from information theory (Shannon 1948), widely adapted for ecological diversity measurement. Results are rounded for display.
How to use this calculator
Enter species counts
Provide the individual count for each species observed in your sample (up to several species).
Read H' and evenness
Both the Shannon index and evenness score solve instantly.
Compare to reference communities
Use the comparison table to judge whether your community shows high or low relative diversity.
Related tools
Frequently asked questions
What is the Shannon diversity index?
The Shannon diversity index (H') is a widely used measure of biodiversity that accounts for both how many species are present (richness) and how evenly individuals are distributed among those species (evenness), calculated as H' = −Σ(pᵢ × ln(pᵢ)).
What values can H' take?
H' is always zero or positive — a value of 0 means only one species is present (no diversity at all), and higher values indicate greater diversity. There's no fixed maximum; it depends on how many species are present and how evenly they're distributed.
What is species evenness, and how is it calculated from H'?
Evenness (E) measures how equally individuals are distributed among species, calculated as E = H'/ln(S), where S is the number of species. E ranges from 0 to 1, with 1 meaning perfectly equal distribution across all species.
Why is the Shannon index preferred over simply counting species?
Simply counting species (richness) ignores how individuals are distributed — a community with 100 individuals of one species and 1 of another has the same richness as one with 50 of each, but feels far less "diverse." The Shannon index captures this difference that a raw species count misses.
Can two very different communities have the same Shannon index?
Yes — H' combines richness and evenness into one number, so a species-poor but perfectly even community can produce a similar H' value to a species-richer but less even one. This is a known limitation, and ecologists often report richness and evenness separately alongside H' for full context.