Tree Diameter Calculator

How to use this calculator

1. Select the units and wrap a measuring tape around each stem at the survey’s specified height.
2. Enter one circumference for a single stem, or a comma-separated list for multiple stems.
3. Enter average bark thickness on one side; use zero to omit the correction.

Formula and method

For the assumptions behind these results, read the explanation below. You can also explore Basal Area and Tree Age.

From a flexible tape to a diameter

A tape can measure around a trunk even when calipers are unavailable. Dividing circumference by π gives the diameter of a circle with that circumference. Real trunks may be oval or irregular, so the result is a circular approximation. Keep the tape level around the measurement plane and avoid pulling it over branches or loose bark.

A bark thickness is measured on one side. The diameter passes through bark on two sides, which is why the correction is twice the thickness. Using one average for all entered stems is an approximation; calculate stems separately if their bark differs substantially. A correction that would leave no wood is rejected.

What the multi-stem equivalent represents

For several stems, the tool squares each diameter, adds those squares, and takes a square root. That gives the diameter of a single circle with the same combined circular area. It is not the physical width across the whole cluster and is not obtained by adding the individual diameters. This area-preserving definition is a stated geometric choice, not a universal forestry or municipal reporting rule.

Forestry protocols differ in how they classify forks, common rootstocks, and stems joined above ground. Decide which stems belong in the same measurement before using the equivalent diameter. Record the method with the result so later surveys can reproduce it. On slopes or leaning trunks, follow the measurement-height and tape-position rules of the survey rather than choosing a different convenient position each time.