Simpson Diversity Index Calculator

Measure species concentration with clear diversity metrics. Compare samples quickly with responsive inputs and charts. Export summaries easily for reports, audits, classes, or projects.

Enter sample data

Use whole-number counts for each species. The page stays single-column, while the form fields adapt to large, medium, and mobile screens.

Species rows

Formula used

Simpson's Dominance Index: D = Σ nᵢ(nᵢ - 1) / N(N - 1)

Simpson Diversity Index: 1 - D

Reciprocal Simpson Index: 1 / D

Evenness: (1 / D) / S

nᵢ is the count for each species, N is the total number of individuals, and S is the number of species with positive counts.

D grows when a few species dominate the sample. The value 1 - D grows when abundance becomes more balanced across species.

How to use this calculator

  1. Enter a dataset name for your record or report.
  2. Choose how many decimal places you want in the output.
  3. Select a sorting mode for the species breakdown table.
  4. Type a species name and its whole-number count in each row.
  5. Add more rows if your sample contains more species.
  6. Click Calculate Diversity to display results above the form.
  7. Review the metrics, table, and Plotly graph for interpretation.
  8. Download CSV or PDF for documentation, reports, or classroom use.

Example data table

Species Count Share (%)
Oak2036.36
Pine1527.27
Maple1018.18
Birch59.09
Cedar59.09

Example output: Total individuals = 55, richness = 5.

Simpson's D: 0.2424

1 - D: 0.7576

1 / D: 4.1250

Evenness: 0.8250

FAQs

1. What does Simpson's D measure?

It measures dominance. Specifically, it estimates the probability that two randomly chosen individuals belong to the same species.

2. Why is 1 - D often preferred?

Because it rises as diversity rises. Many people find higher-is-better interpretation easier when comparing samples.

3. Can I use zero-count species rows?

Yes. Zero rows can remain in the form, but they are excluded from richness and index calculations.

4. Should counts be decimals?

No. This calculator expects whole-number counts because Simpson's index is based on observed individuals, not proportions entered directly.

5. What does the reciprocal index mean?

It approximates the number of equally common species that would produce the same dominance level. Larger values suggest greater effective diversity.

6. What is evenness here?

Evenness compares effective diversity with species richness. Values closer to 1 suggest counts are spread more evenly across species.

7. Can this compare two habitats?

Yes. Run each habitat separately, then compare D, 1 - D, reciprocal index, richness, and the species share chart.

8. Where is this index useful?

It is common in ecology, microbiology, conservation, forestry, classrooms, and any study that evaluates concentration across categories.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.