How this calculator works
The growth-factor shortcut multiplies diameter in inches by a species factor expressed in years per inch. The listed worksheet factors are broad forest-grown estimates. Competition, pruning, water and growing conditions can change diameter growth greatly; a large tree need not be old. The calibration mode derives a local effective factor from a tree of known age. A properly cross-dated core is a stronger age measurement.
Formula
Estimated years = diameter in inches x growth factor; diameter = circumference/pi; factor = known years / diameter in inches.
Worked example
An 18 inch cottonwood diameter at factor 2 gives an estimated 36 years. A 20 inch white oak at factor 5 gives 100 years.
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Frequently asked questions
How accurate is this estimate?
It has no universal error bound. Local growth history can make a species shortcut substantially wrong.
Can I date a street tree?
Use a known planting date when available. Street conditions often differ from the forest conditions behind the factors.
Why are the factors in years per inch?
The cited worksheet defines them against inch diameters. Metric inputs are converted to inches before multiplication.