Gut Microbiome Score Calculator

Enter the relative abundance of four major gut phyla to compute the Shannon diversity index, Simpson's diversity index, Pielou's evenness, and the Firmicutes/Bacteroidetes ratio.

Quick Facts

Shannon index
H' = -sum(pi x ln(pi))
For 4 phyla, H' ranges from 0 (one phylum dominates) to ln(4) is about 1.386 (perfectly even).
Pielou's evenness
J' = H' / ln(4)
Scales the Shannon index to a 0-1 balance score.
F/B ratio
Firmicutes % / Bacteroidetes %
A commonly reported summary metric in 16S rRNA gut microbiome studies.

Your Results

Calculated
Shannon diversity index (H')
-
Range: 0 to ln(4) is about 1.386
Simpson's diversity index (1-D)
-
Range: 0 to 0.75
Pielou's evenness (J')
-
Range: 0 (skewed) to 1 (even)
Firmicutes/Bacteroidetes ratio
-
F/B ratio

Ready

Enter your phylum-level relative abundances, then calculate the diversity indices.

About the Gut Microbiome Score Calculator

This tool applies standard community-ecology diversity formulas to the phylum-level composition of a gut microbiome sample. Enter the relative abundance (as a percentage) of the four phyla that typically make up most of the human gut microbiota - Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria - and the calculator reports the Shannon diversity index, Simpson's diversity index, Pielou's evenness, and the Firmicutes/Bacteroidetes (F/B) ratio.

How the diversity indices are calculated

The four entered percentages are first converted into proportions pi by dividing each by their sum. From those proportions the calculator computes: the Shannon diversity index H' = -sum(pi x ln(pi)), which is 0 when a single phylum makes up essentially the whole sample and reaches its maximum of ln(4), about 1.386, when all four phyla are equally represented; the Simpson diversity index (1-D) = 1 - sum(pi^2), which behaves similarly and ranges from 0 to 0.75 for four categories; and Pielou's evenness J' = H' / ln(4), which rescales the Shannon index to a 0-1 balance score. The Firmicutes/Bacteroidetes ratio is simply the Firmicutes percentage divided by the Bacteroidetes percentage.

Interpreting the numbers

  • These are descriptive diversity statistics from ecology and microbiology, not a diagnostic score - there is no universally agreed "healthy" cutoff for any of them.
  • Real gut microbiome samples contain far more than four phyla and many more taxa within each phylum. This calculator works at the phylum level for simplicity, so it summarizes only part of the full community structure.
  • The Firmicutes/Bacteroidetes ratio is frequently reported in the research literature, but its relationship to specific health outcomes is still actively debated and should not be treated as settled.

Important disclaimer

This calculator performs descriptive-statistics arithmetic on the numbers you provide. It does not analyze a biological sample, does not diagnose any condition, and is not a substitute for stool testing or advice from a qualified healthcare provider or registered dietitian.

Frequently Asked Questions

What formula does the Gut Microbiome Score Calculator use?
It converts the relative abundance you enter for four major gut phyla (Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria) into proportions and applies standard community-ecology formulas: the Shannon diversity index H' = -sum(pi x ln(pi)), the Simpson diversity index (1-D) = 1 - sum(pi^2), and Pielou's evenness J' = H' divided by ln(4). It also reports the Firmicutes-to-Bacteroidetes ratio.
What is a good Shannon diversity index for gut bacteria?
With four categories the Shannon index ranges from 0, when one phylum makes up essentially all of the sample, to a maximum of ln(4) which is about 1.386, when all four phyla are equally represented. Higher values indicate a more even phylum-level distribution. This is a descriptive diversity measure, not a diagnostic threshold.
What does the Firmicutes/Bacteroidetes ratio mean?
The Firmicutes/Bacteroidetes (F/B) ratio is simply the Firmicutes percentage divided by the Bacteroidetes percentage. It is widely reported in 16S rRNA gut microbiome studies as a summary of the balance between these two dominant phyla, but its links to specific health outcomes are still debated in the research literature, so treat it as descriptive rather than diagnostic.

Related calculators