Find a tree trunk diameter, radius and basal area from its circumference, measured with a tape around the trunk.
Result
How to use this tool
Wrap a tape around the trunk at 4.5 ft above ground.
Enter the reading in inches.
Diameter, radius and basal area appear instantly.
Feed the diameter into basal area or growth-factor estimates.
Formula & worked example
A trunk circumference of 62.83 inches means a diameter of 20 inches.
Limitations — read this before you rely on it
Assumes a circular trunk. Buttress roots, flares and lean make the diameter approximate.
Frequently asked questions
Diameter at breast height, the standard forestry measurement at 4.5 ft.
For a circle, circumference = π × diameter.
The result is an average-equivalent diameter, not exact.
Yes: divide the centimetre circumference by π for diameter in centimetres.
4.5 ft (1.37 m) above ground on the uphill side of a slope.