How do you find tree diameter from circumference?

Landscape & Site WorkForestry & ISA Standards

Tree Diameter (DBH) & Basal Area Calculator

Convert tree trunk circumference into Diameter at Breast Height (DBH), calculate cross-sectional basal area, and estimate mature tree age.

Landscape & Site Work Field StandardsForestry & ISA Standards

Engineering formulations calibrated to IPC, UPC & NEC specificationsSub-Zero Cold Climate Tolerances

Quick Summary & Key Answer

To calculate tree diameter (DBH), divide the trunk circumference measured at 4.5 feet above the ground by π (3.14159). For example, a tree with a 48-inch circumference has a DBH of 15.28 inches. Multiply DBH by the species growth factor to estimate tree age.

DBH stands for Diameter at Breast Height (standard 4.5 feet above ground).
The critical root zone extends 1.5 feet outwards for every 1 inch of DBH.
Basal Area (sq ft) = 0.005454 × DBH².

Interactive Calculator

Adjust inputs for real-time results

Trunk Circumference at 4.5 ft (Breast Height)inches

inches

Tree Species (Growth Factor)

Calculated OutputISA Standard Measured

Diameter at Breast Height (DBH)

15.3"inches

Estimated Tree Age: 76 Years
Trunk Basal Area: 1.27 sq ft
Crown Drip-Line Root Radius: 22.9 ft from trunk

Note: DBH is measured at exactly 4.5 feet (1.37 meters) above ground level on the uphill side of the tree.

How to Measure DBH Accurately

Wrap a flexible measuring tape around the trunk 4.5 feet above grade; if swelling or branch forks occur at 4.5 ft, measure just below the swell.

Frequently Asked Questions

Common questions regarding this calculation and code compliance

Divide circumference by 3.14159 (Diameter = Circumference ÷ π).