Tree Age Calculator
Get a rough age from trunk size using a published species growth factor, or record a ring count. Trunk size is not an exact age measurement — the result is a ballpark.
Before you start
Method : DBH × species growth factor (rough), or ring count.
Checked : unit conversions and worked examples tested; sources checked 5 October 2026. Factor tables have no published error range.
Review : not reviewed by an arborist or forester.
Your entries stay in this browser tab; nothing is sent or stored.
Enter a trunk measurement and species, or a ring count.
How to Use This Calculator
- Measure the trunk at 4.5 ft (1.37 m) above ground
- Enter circumference or diameter in inches or cm and pick the species
- Or switch to ring count
Methodology & assumptions
DBH (diameter at breast height, 4.5 ft) = circumference ÷ π. Centimetres are converted at 2.54 cm per inch. Age ≈ DBH (in) × species growth factor (years per inch). Supported DBH 1–120 in.
Factors are from an ISA-attributed table compiled by Allegheny County Parks (from the 1988 "Bicentennial Trees of Allegheny County"). They describe typical forest-grown trees in the eastern/Midwest US; they are not peer-reviewed models and give no error range.
Worked examples
White oak — not listed: Purdue's worked example uses 70 in circumference → 22 in DBH × 5.0 = 110 years (83 after the urban −25%).
Sugar maple, 100 cm circumference: 39.37 in ÷ π = 12.5 in × 5.5 = ~69 years.
Silver maple, 20 in diameter: 20 × 3 = 60 years.
Understanding your result
Treat the number as an order-of-magnitude guide. Woodland trees widen about half as fast as open-grown ones (Purdue), so the same trunk can mean very different ages.
Sources & further reading
- How Old Is My Tree? — Lindsey Purcell, Purdue Landscape Report, 10 April 2018Method, white-oak example, −25% urban adjustment (anecdotal), woodland vs open-grown growth. Checked 5 October 2026.
- How to Age a Living Tree — Allegheny County Parks (Latodami)Species growth-factor table (ISA-attributed; compiled 2016, updated 2021).
- Smith KT. Big trees, old trees, and growth factor tables. Tree Care Industry, Feb 2018 (USDA Forest Service)Explains why growth-factor ages are unreliable for large old trees.
Frequently Asked Questions
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