Shannon Diversity Index Calculator

What this calculator does

The Shannon diversity index (often written as H′ or H) is a widely used ecological diversity metric that combines:

• Richness: how many species (or categories) are present, and
• Evenness: how evenly individuals are distributed among those species.

This page lets you paste a list of species counts (abundances) and computes Shannon diversity using the natural logarithm (ln). It can also report the effective number of species (e^H′), which converts the index into an intuitive “equivalent” number of equally common species.

How to use

1. Enter the counts for each species (e.g., 10, 6, 4, 20). You can typically separate values with commas, spaces, or new lines.
2. Click Calculate.
3. Interpret results by comparing sites/samples measured with the same sampling method and effort.

Formula (Shannon index)

Let there be S species with counts n_i, total abundance N = ∑_i=1^S n_i, and proportions:

p_i = n_i / N

The Shannon diversity index (using natural log) is:

Effective number of species (also called the “true diversity” of order 1) is:

D₁ = e^H′

Interpreting the results

• H′ increases when you add species (higher richness) and/or when abundances become more even (higher evenness).
• H′ = 0 when there is only one species with all individuals.
• H′ is not inherently capped: practical ranges depend on the system, taxonomic resolution, sample size, and the log base used. Statements like “0 to 4–5” are only rough, context-dependent observations.
• e^H′ is often easier to compare: for example, if e^H′ = 5, the community’s diversity is equivalent to five equally common species.

Rule-of-thumb categories (use with caution)

Some practitioners use broad heuristics to quickly summarize Shannon values, but these are not universal thresholds and should not replace within-study comparisons:

Worked example

Counts: A = 10, B = 6, C = 4, D = 20.

Total N = 10 + 6 + 4 + 20 = 40, so proportions are:

• p_A = 10/40 = 0.25
• p_B = 6/40 = 0.15
• p_C = 4/40 = 0.10
• p_D = 20/40 = 0.50

Compute H′ = −∑ p_i ln(p_i):

• −(0.25 ln 0.25) ≈ 0.3466
• −(0.15 ln 0.15) ≈ 0.2846
• −(0.10 ln 0.10) ≈ 0.2303
• −(0.50 ln 0.50) ≈ 0.3466

Sum ≈ 1.208. So H′ ≈ 1.21. The effective number of species is e^1.21 ≈ 3.35, meaning the community’s diversity is similar to ~3.35 equally common species.

For comparison, if all 4 species were perfectly even (10 each out of 40), then H′ = ln(4) ≈ 1.386.

Assumptions & limitations

• Counts must be non-negative. Negative values are not meaningful for abundance data.
• Zero counts: species with n_i = 0 contribute nothing because p_i = 0 and the limit of p ln p as p → 0 is 0. In practice, calculators typically ignore zero terms.
• Log base matters: this calculator uses ln. Using log base 2 or 10 rescales H′ but does not change rank-order comparisons within the same base.
• Sampling effort & comparability: H′ depends on how completely you sampled the community. Compare sites only when methods (area, time, trap type, sequencing depth, etc.) are consistent.
• Taxonomic/category definition: “Species” can mean true species, OTUs/ASVs, functional groups, land-use classes, etc. Different resolutions change the value.
• Does not identify significance: a difference in H′ between two samples is descriptive; statistical testing typically requires resampling/bootstrapping or specialized tests.

References

• Shannon, C. E. (1948). A Mathematical Theory of Communication. Bell System Technical Journal.
• Magurran, A. E. Measuring Biological Diversity. (Standard reference on diversity indices and interpretation.)
• Jost, L. (2006). Entropy and diversity. Oikos (effective number of species / true diversity framing).