Biodiversity Index Calculator
Calculate Shannon-Wiener, Simpson's, and Margalef biodiversity indices from species count data for conservation assessment.
About this calculator
This calculator computes several standard ecological diversity indices from a species count survey -- the kind of data collected in a quadrat, transect, or plot-based biodiversity assessment. The Shannon-Wiener Index (H'), whose entropy formula traces to Claude Shannon's 1948 paper "A Mathematical Theory of Communication" (Bell System Technical Journal), is the headline output, a widely used measure that combines both how many species are present (richness) and how evenly individuals are distributed across those species (evenness); it rises with more species and falls when one or a few species dominate the count. Total species count has the largest single effect on the Shannon-Wiener Index of any input here, since richness is one of the two direct components the index measures, while the count of individuals belonging to the single most abundant species pulls the index down as that species' share of the total grows -- a community dominated by one species is, by definition, less diverse than one where individuals are spread evenly.
Simpson's Diversity and its reciprocal offer an alternative diversity measure that weights dominant species more heavily than Shannon-Wiener does, while Margalef's Richness Index and species density both normalize species count by sample size or area so surveys of different scope can be compared more fairly. Pielou's Evenness (J) isolates the distribution component alone, on a 0-1 scale where 1 means every species was represented in exactly equal numbers. Sample area and number of habitat types don't feed into the core diversity indices at all -- sample area is used only for species density and the species-area extrapolation, and habitat type count only feeds the separate habitat diversity correlation score, so changing either one leaves Shannon-Wiener, Simpson's, and Berger-Parker completely unchanged.
Inputs
Results
Shannon-Wiener Index (H')
3.11
Biodiversity Rating
High Biodiversity
Figures current as of 1966. Sources: Shannon, C.E. "A Mathematical Theory of Communication." Bell System Technical Journal, 1948;27:379-423., Simpson, E.H. "Measurement of Diversity." Nature, 1949;163:688., Pielou, E.C. "The measurement of diversity in different types of biological collections." Journal of Theoretical Biology, 1966;13:131-144.
How to Use This Calculator
- Enter the total species count (S) and total individual organisms counted (N) in your sample.
- Input the count of the most abundant (dominant) species.
- Set the sample area and number of distinct habitat types.
- Review the Shannon-Wiener Index (H') and Simpson Diversity to characterize biodiversity.
- Use the evenness score to assess how evenly individuals are distributed across species.
How the result changes with Total Species Count (S)
| Total Species Count (S) | Shannon-Wiener Index (H') | Biodiversity Rating |
|---|---|---|
| 13 | 2.53 | High Biodiversity |
| 19 | 2.87 | High Biodiversity |
| 38 | 3.47 | High Biodiversity |
| 63 | 3.91 | Very High Biodiversity |
What each input means
- Total Species Count (S)
- Number of distinct species observed in the sample.
- Total Individuals (N)
- Total number of individual organisms counted across all species.
- Most Abundant Species Count
- Number of individuals of the most abundant species. Used to calculate dominance indices.
- Sample Area
- Total area surveyed.
- Number of Habitat Types
- Number of distinct habitat types present (forest, wetland, grassland, etc.).
What each result means
- Shannon-Wiener Index (H')
- Typical range 1.5-3.5. Higher = more diverse.
- Simpson's Diversity (1-D)
- 0-1 scale. Higher = more diverse.
- Pielou's Evenness (J)
- 0-1 scale. 1 = perfectly even distribution.
- Berger-Parker Dominance
- Proportion of the most abundant species. Lower = more even.
- Habitat Diversity Score
- Correlates habitat type count against species richness. 0-100 scale.
How this is calculated
Worked example, using the default values
- Identify Input Parameters5 parametersTotal Species Count (S) = 25, Total Individuals (N) = 500, Most Abundant Species Count = 80, Sample Area = 10, Number of Habitat Types = 4 = 5 input(s) provided
- Calculate Shannon-Wiener IndexShannon-Wiener Index3.109 = 3.109
- Calculate Biodiversity RatingBiodiversity Rating = tier based on Shannon-Wiener Index (H') thresholdsHigh Biodiversity = High Biodiversity
- Calculate Simpson's DiversitySimpson's Diversity0.945 = 0.945
- Calculate Simpson's ReciprocalSimpson's Reciprocal18.18 = 18.18
Figures and sources
- Shannon entropy formula (H' = -Σ pᵢ ln pᵢ), the basis of the Shannon-Wiener Index (1948) — Shannon, C.E. "A Mathematical Theory of Communication." Bell System Technical Journal, 1948;27:379-423.
- Simpson's Diversity Index (1949) — Simpson, E.H. "Measurement of Diversity." Nature, 1949;163:688.
- Pielou's Evenness (J) (1966) — Pielou, E.C. "The measurement of diversity in different types of biological collections." Journal of Theoretical Biology, 1966;13:131-144.
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does total species count have the biggest effect on the Shannon-Wiener Index?
Species richness -- the raw count of distinct species observed -- is one of the two direct inputs the Shannon-Wiener formula measures, alongside how evenly individuals are spread across those species. Because richness enters the calculation directly and total individuals or dominant species count only shift the evenness component, a change in total species count typically moves the index more than an equivalent percentage change to the other survey numbers.
Why don't sample area or habitat type count affect the Shannon-Wiener or Simpson's diversity results?
Shannon-Wiener, Simpson's Diversity, and Berger-Parker Dominance are all calculated purely from species counts and individual counts -- how many species, how many total individuals, and how many individuals belong to the dominant species -- with no area or habitat term in their formulas. Sample area only feeds into the separate Species Density and Predicted Species (2x area) outputs, and habitat type count only feeds the Habitat Diversity Score, so those two inputs can change freely without moving the core diversity indices at all.
Why does a higher dominant species count lower the Shannon-Wiener Index?
The Shannon-Wiener Index rewards even distribution across species, so when one species accounts for a larger share of the total individual count, the community is by definition less evenly distributed, which the formula reflects as a lower index value. This is the same underlying reason the Berger-Parker Dominance Index rises as dominant species count rises -- both indices are capturing the same real-world pattern of one species crowding out the rest, just on different mathematical scales.
What's the difference between Simpson's Diversity and Shannon-Wiener?
Both combine richness and evenness into a single diversity number, but Simpson's Diversity -- introduced by E.H. Simpson in his 1949 Nature paper "Measurement of Diversity" -- weights the most abundant species more heavily, making it more sensitive to dominance by one or a few common species, while Shannon-Wiener is more sensitive to the presence of rare species and overall species richness. Ecologists often report both together, along with Pielou's Evenness (J) -- from E.C. Pielou's 1966 Journal of Theoretical Biology paper, which isolates the distribution component of Shannon-Wiener alone -- because together they can tell different stories about the same community: a habitat can score moderately on one index while scoring quite differently on the others if it has many rare species alongside one dominant one.
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