The growth factors behind the tree age estimator: years per inch of trunk, by species

A tree’s age can be estimated from its trunk: measure the diameter at 4.5 feet, in inches, and multiply by a growth factor for the species. The table below holds every factor the tree age estimator knows, for 88 species, with the source of each and whether the estimator applies it.

How to read the table

The factor is years of age per inch of trunk diameter for a tree grown in the open. A red maple with a 20-inch trunk and a factor of 4.5 is about 90 years old; a forest-grown tree, which thickens more slowly, is older than the factor says.

Blue Whale Trees applies Purdue Extension’s chart where it lists the species, and the second column holds those figures. Factors from other sources stand in the third column for comparison and are not applied, so a species with several shows how far the published figures differ.

Sixty-five of the species are trees we grow, and a name opens the plant’s page; the rest are common natives the estimator takes as well.

Growth factors, A to Z

The table holds 125 factors for 88 species, 19 of them applied.

The table as a file

Download the table as CSV or JSON: 125 rows, one for one growth factor from one source for one species, with the columns below. The figures are published under the Creative Commons Attribution 4.0 licence: use them with a credit to bluewhaletrees.com and a link to this page. Updated 2026-10-22.

What each column means

• species: the species id the tree age estimator uses: a plant page’s address word, or the id of a common native the nursery does not grow
• name: the common name
• botanical: the botanical name
• in_catalog: true where the nursery grows the species and it has a plant page
• factor: the growth factor: the years of age for each inch of trunk diameter at 4.5 feet, for a tree grown in the open
• used: true where the estimator applies this factor; false where the figure is recorded for comparison and not applied
• kind: chart where the source prints a table of factors, text where it gives the figure in prose
• source: the publisher’s short name
• source_name: the source as the estimator’s page cites it
• url: its address

How the table is made

The estimator applies Purdue Extension’s growth factors for the species that chart lists, as the tree age tool states. Figures from the other sources are recorded beside them for comparison and not applied. The files are written from the records and checked at every release.

Cite this page

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<a href="https://bluewhaletrees.com/articles/tree-age-factors/">Growth factors: the years per inch of trunk the tree age estimator uses, by species</a>, Blue Whale Trees, updated October 22, 2026.

Blue Whale Trees. (2026, October 22). Growth factors: the years per inch of trunk the tree age estimator uses, by species. https://bluewhaletrees.com/articles/tree-age-factors/

Common questions

How do I estimate a tree’s age from its trunk?

Measure around the trunk at 4.5 feet, divide by 3.14 for the diameter in inches, and multiply by the species’ factor. The estimator does the arithmetic and gives a range.

Which trees age fastest per inch?

The lowest factor the estimator applies is 2 for eastern cottonwood, the highest 7.5 for shagbark hickory. A low factor means a fast-thickening trunk, so the same girth means a younger tree.

Why are some factors not applied?

The estimator applies one chart, Purdue’s, so that every answer rests on the same method. The other sources’ figures are kept in the table for comparison.

Does the factor work for a forest tree?

No; a forest-grown tree thickens more slowly and is older than the open-grown factor says. The estimator asks where the tree grew and adjusts.