Shannon Diversity Index Calculator
Shannon H, evenness and effective species from counts.
Result
Shannon index, H: 1.029653
Describes this sample only. Rare species a sample missed are not in it, so a bigger sample usually finds a higher H.
- Largest possible H for this many species
- 1.098612
- Evenness, J
- 0.937231
- Effective number of species
- 2.800094
- Species present
- 3
- Total individuals
- 100
https://calcgallery.com/statistics/shannon-diversity-index-calculator/
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How to use the Shannon Diversity Index Calculator
- Enter one row per species with the number of individuals counted, or another abundance such as percent cover.
- Choose the logarithm, natural log unless your course or paper uses base 2 or base 10.
- Read H, the evenness, the largest H possible with that many species, and the effective number of species.
The formulas
pᵢ = nᵢ ÷ N share of species iH = −(p₁ log p₁ + p₂ log p₂ + … + p_S log p_S)H max = log S all species equally commonJ = H ÷ ln S evenness (natural logs on both)effective number of species = e^H (with H in natural logs)S is the number of species with a count above zero and N the total count. A species with a count of zero contributes nothing to H and is not counted in S.
What the diagram shows
Each species’ share of the sample as a bar, from the most common to the least. The flatter the row of bars, the higher the evenness.
With your numbers
- H = −(0.5 ln 0.5 + 0.3 ln 0.3 + 0.2 ln 0.2) = 1.029653 in natural logs
Quick reference
Describes this sample only. Rare species a sample missed are not in it, so a bigger sample usually finds a higher H.
| Example | Shannon index, H |
|---|---|
| 50, 30 and 20 | 1.029653 |
| Four species, 10 each | 1.386294 |
| One species only | 0 |
| Two equal species, in bits | 1 |
| 50, 30 and 20 in base 10 | 0.447173 |
| Eight species, 35 down to 2 | 1.763607 |
Common questions about the Shannon Diversity Index Calculator
- What does the Shannon index measure?
- How hard it is to predict the species of the next individual you pick from the sample. It rises with the number of species and with how evenly the individuals are shared among them. A sample of 50, 30 and 20 individuals of three species has an H of about 1.03 in natural logs.
- Which logarithm should I use?
- Whichever the work you are comparing with uses; ecology most often uses the natural log. Changing the base only rescales H: the same sample is about 1.03 in natural logs, 1.49 in base 2 and 0.45 in base 10. Evenness and the effective number of species come out the same in every base, which makes them easier to compare.
- What are evenness and the effective number of species?
- Evenness, Pielou's J, is H divided by the largest H possible for that many species, ln S, so it runs from near 0 when one species dominates to 1 when all are equally common. The effective number of species, e to the power H, is how many equally common species would give the same H: about 2.8 for the 50, 30 and 20 sample.
- Can I compare H between two samples?
- With care. H depends on how hard you looked: a bigger sample tends to find rarer species and a higher H. Compare samples collected the same way and of similar size, and remember that the index describes the sample, not the whole habitat.