Tree Age Calculator — From Trunk Circumference
Estimate tree age from trunk circumference, species and growing conditions. See the diameter and the illustrative growth factors behind the estimate.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
Measure around the trunk at chest height, using the selected cm or inch unit. This model converts circumference to diameter and applies fixed species and condition factors. Both the age and the displayed range are illustrative estimates, not a measured age or a statistical confidence interval.
Worked example
calculated with the default values below
Trunk circumference at chest height 150 cm · Measurement unit cm · Species Oak · Growing conditions Average Estimated age 75 years · Illustrative model range 56-98 years · Trunk diameter 47.7 cm · Trunk diameter 18.80 in · Combined factor (years per inch) 4.0
Method and assumptions
Divide circumference in inches by π to find trunk diameter. Multiply diameter by the species factor and the condition multiplier: age = diameter × g × c. The combined factor shown in the results is g × c, not g alone. This model uses species factors of 2–7 and condition multipliers of 0.85, 1 or 1.25; these are illustrative presets rather than measured growth rates for the individual tree. The range is 0.75 to 1.3 times the estimate, rounded to years. It is not a confidence interval. For a 150 cm oak trunk with average conditions, the estimate is about 75 years and the illustrative range is 56–98 years. Results depend on the presets and cannot determine an exact planting date.
Data sources
Illinois Extension describes circumference-based age estimates and their uncertainty. It does not validate this tool’s complete preset table, condition multipliers or illustrative age range.
Disclaimer
These are general gardening estimates. Planting windows, growth, water and nutrient needs vary by place and plant. Check local extension guidance and product labels before acting on an estimate.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
A = C ÷ π × g × c
- A
- Estimated age (years)
- C
- Trunk circumference (in)
- g
- Species growth factor
- c
- Condition factor
The 2–7 species factors and 0.85/1/1.25 condition multipliers are illustrative heuristics, not measured growth rates for an individual tree. The 0.75A–1.3A range is also heuristic. Enter circumference in the unit selected above; the calculation converts centimetres to inches.
Frequently asked questions
How reliable is the tree-age estimate and its displayed range?
Treat both as rough model outputs. Diameter is circumference divided by π, then age is diameter in inches multiplied by a species factor and a condition multiplier. For this model, oak is 4, apple 7 and willow 2; good, average and poor conditions multiply by 0.85, 1 and 1.25. The displayed factor combines both choices. The range uses 0.75–1.3 times the estimate and is not a statistical confidence interval. For a 150 cm oak in average conditions, the model gives about 75 years and a 56–98 year range. Local growth, species variation and tree history can make the actual age different.