Shannon Diversity Index Calculator
Measure community diversity from species counts, with richness, evenness, total abundance, a population breakdown, and a validated Excel export.
Community counts
Natural log is the common ecological convention; base 2 and base 10 rescale H without changing the abundance proportions.
Use whole nonnegative counts. Blank rows are ignored; a zero count is treated as an observed category with no individuals and does not add to richness.
Results
H is 1.33 with richness 5 and evenness 0.824.
Relative abundance
The largest sample group contains 48.0% of all individuals. A more even ring generally corresponds to higher evenness.
Population breakdown
| Population | Individuals | Proportion | H contribution |
|---|---|---|---|
| Population 1 | 5 | 20.00% | 0.322 |
| Population 2 | 12 | 48.00% | 0.352 |
| Population 3 | 2 | 8.00% | 0.202 |
| Population 4 | 5 | 20.00% | 0.322 |
| Population 5 | 1 | 4.00% | 0.129 |
Each H contribution equals – p × log(p) in the selected logarithm base. Contributions sum to the displayed Shannon index; zero-count and blank rows contribute nothing.
How to use the Shannon diversity index calculator
What this calculator does
This calculator summarizes diversity within one sampled community from counts of individuals in separate populations or species. It combines two ideas that simple species counts do not capture on their own: how many nonzero populations are present, called richness, and how evenly individuals are distributed among those populations. The main result is the Shannon diversity index, H. The calculator also reports evenness, total individuals, average population size, and the row-by-row contribution of each population. It is a descriptive index of the data you enter; it does not prove that a habitat is healthy, compare sampling quality, or correct for species that were missed during field collection.
When to use it
Use the calculator when comparing community composition across sampling plots, dates, restoration sites, habitats, or treatment groups that were surveyed with reasonably comparable methods. It is also useful in class exercises that show why two communities can have the same richness but different diversity when one community is dominated by a single population. The National Park Service explains biodiversity in terms of both species richness and abundance or evenness, which is the same conceptual distinction captured by this calculation.
How to calculate
The calculator opens with a ready-to-use five-population demonstration and an immediately available validated Excel workbook. To replace the example with your own sample:
- Choose the Logarithm base. Natural logarithm is the common ecological convention and is the default.
- Replace each Population count with the whole number of individuals observed in that group. Add rows for additional groups, up to 40, or remove rows you do not need.
- Read Shannon diversity index (H) together with Evenness (E) and Richness. The table shows the proportion and H contribution for every nonblank row.
- Use Download Excel to export the current counts and calculated values. The workbook is generated from the same current model used on screen.
- Use Reset when you want to clear the demonstration. Reset returns to three blank population rows and natural logarithm, clears the results, and disables Excel export until at least one valid positive count is entered again.
Input guide
Logarithm base
This required selector accepts natural logarithm (e), base 2, or base 10. The demonstration uses natural log. Changing the base rescales H and each row's H contribution, but it does not change proportions, richness, total individuals, or evenness because H and its maximum are rescaled together. When comparing samples, use the same base for every sample.
Population counts
Each Population field accepts a whole nonnegative count from 0 to 1,000,000,000,000. Commas are allowed only as standard thousands separators, so 1,250 is valid while 1,25, 1.5, 1e3, and negative values are rejected. Blank rows are ignored. A zero is allowed but contributes neither richness nor H. The sample uses 5, 12, 2, 5, and 1. Increasing a rare population can increase evenness; increasing an already dominant population can reduce evenness.
Output guide
Shannon diversity index (H) is the sum of each population's information contribution, shown in the selected log base. Zero means only one nonzero population is present. Higher values can result from greater richness, greater evenness, or both, so H should be interpreted with the accompanying metrics rather than against a universal ecological cutoff. Evenness (E) is H divided by the maximum H possible for the observed richness; it ranges from 0 to 1 when richness is at least two, and 1 represents equal proportions. For richness of one, evenness is mathematically undefined and is shown that way rather than forcing a value. Richness is the exact count of populations with more than zero individuals. Total individuals is the exact sum of all valid counts. Average population size is total individuals divided by richness.
The Relative abundance donut uses the same population proportions shown in the table. With more than five nonzero populations, it keeps the four largest populations and combines the remainder as Other so the part-to-whole comparison stays readable. The Population breakdown columns show the population label, exact individual count, proportion of the total, and H contribution. Proportions sum to 100% across nonzero populations, and H contributions sum to H.
Worked example
The demonstration contains counts of 5, 12, 2, 5, and 1, for a total of 25 individuals and richness 5. Their proportions are 0.20, 0.48, 0.08, 0.20, and 0.04. With natural logarithms, H is – Σ[p × ln(p)] = 1.3268936936, displayed as 1.33. The maximum possible H for five equally abundant populations is ln(5) = 1.6094379124, so evenness is 1.3268936936 ÷ 1.6094379124 = 0.8244454063, displayed as 0.824. The average population size is 25 ÷ 5 = 5.00. The Open University provides a concise educational example of the same Shannon-index calculation from relative abundance.
Learn more
For an applied environmental example, the U.S. Environmental Protection Agency's archived landscape metric documentation explains how a Shannon-Wiener index rises as diversity of land-cover types increases and why a single category produces an index of zero.
How the Shannon index works
H = – Σ(pᵢ × log(pᵢ)), where pᵢ = nᵢ / N
For each nonzero population, the calculator divides its count n by the total count N to obtain p. A population with a large share of the sample has a large p, while a rare population has a small p. The term – p × log(p) is always nonnegative for proportions between zero and one. Adding those contributions gives H. When all observed populations are equally abundant, H reaches its maximum for that richness: log(k), where k is the number of nonzero populations.
Evenness standardizes H against that maximum. This helps distinguish a high H caused mainly by many species from a high H caused by a very balanced distribution. Because the log base multiplies both H and log(k) by the same conversion factor, evenness is unchanged when the base changes. That is why the base is important for reporting H itself but does not alter the underlying ranking of populations or the E result.
Common interpretation mistakes
A larger H is not automatically “good” and a smaller H is not automatically “bad.” Some ecosystems naturally contain a few dominant species, while disturbance can sometimes raise apparent local richness by mixing communities. Another common mistake is to compare H values computed with different logarithm bases without converting them. Finally, do not read evenness as richness: a community with two equally abundant populations can have E = 1 even though its richness is only two. The breakdown table is therefore useful because it keeps the index tied to the counts and proportions that created it.