What Is Simpson's Biodiversity Index Calculator?
Simpson's Diversity Index is one of the most widely used measures of biodiversity in ecology. It combines species richness (how many species are present) and evenness (how evenly individuals are distributed across those species) into a single number between 0 and 1. This calculator takes species counts from a sample and computes that index automatically.
Ecologists use Simpson's Index to compare biodiversity between sites, track changes over time, or evaluate the effects of habitat disturbance or restoration.
How to Read Your Results
Simpson's Diversity Index (D)
Ranges from 0 (no diversity — a single species dominates completely) to just under 1 (very high diversity — individuals are spread evenly across many species). Higher values indicate a more diverse sample.
Species Richness
The simple count of how many different species appear in the sample (with a count greater than zero) — the "how many kinds" part of biodiversity, without accounting for evenness.
Total Individuals (N)
The sum of individuals counted across all species entered.
Dominance Index (λ)
The complement of D (λ = 1 − D), representing the probability that two randomly chosen individuals belong to the same species. Higher dominance means lower diversity.
Real-World Example
A pollinator survey counts five species in a meadow plot: 45 individuals of Species A, 30 of Species B, 12 of Species C, 8 of Species D, and 3 of Species E.
| Species | Count (n) |
|---|---|
| Species A | 45 |
| Species B | 30 |
| Species C | 12 |
| Species D | 8 |
| Species E | 3 |
| Total (N) | 98 |
With these counts, Simpson's Index works out to roughly D ≈ 0.68 — indicating moderately high diversity, though Species A and B together still dominate the sample.
Tips for Sampling Biodiversity
- Use consistent sampling effort (same trap-hours, plot size or survey time) whenever you compare two samples.
- A high species count alone doesn't guarantee a high index — one dominant species can pull D down even with many species present.
- Combine with species richness to distinguish "many species, uneven" sites from "many species, even" sites.
- Repeat sampling across seasons for a more reliable picture, since single-visit counts can be noisy.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team