Conversion July 13, 2026 · 8 Min Read

Tree Diameter Calculator – Guide & Formulas

Convert tree circumference to diameter (DBH). Calculate diameter at breast height from circumference measurements for forestry and arboriculture.

Convert tree circumference measurements to diameter at breast height (DBH). Essential for forestry surveys, arboriculture assessments, and timber cruising.

Key Takeaway

Use the free Tree Diameter Calculator to convert tree circumference to diameter (dbh). calculate diameter at breast height from circumference measurements for forestry and arboriculture. Get instant results with step-by-step explanations.

How to Use the Tree Diameter Calculator

  1. Choose to enter either circumference or diameter measurement.
  2. Enter the circumference measured at breast height (4.5 ft / 1.37 m).
  3. Select the unit system (inches, feet, centimeters, or meters).
  4. Review the calculated DBH and corresponding basal area.

The Formula

Diameter (DBH) = Circumference / π. Where π ≈ 3.14159. For circumference in inches, DBH is in inches.

Variable Definitions

  • DBH: Diameter at Breast Height — the standard measurement point for tree diameter (4.5 ft / 1.37 m above ground)
  • Circumference: The distance around the tree trunk at breast height
  • π: Pi — the mathematical constant approximately equal to 3.14159

Converting 37.7-inch Circumference to DBH

Calculate DBH from a circumference measurement of 37.7 inches.

  1. Step 1: Identify circumference = 37.7 inches.
  2. Step 2: Apply formula: DBH = 37.7 / π.
  3. Step 3: Calculate: 37.7 / 3.14159 = 12.0 inches.
  4. Step 4: The tree has a DBH of 12 inches.

Frequently Asked Questions

Why measure at breast height?

Breast height (4.5 feet / 1.37 m) is the international standard for tree diameter measurement. It avoids irregularities at the base (buttress roots, flaring) and provides consistent, comparable measurements.

What tool measures tree circumference?

A diameter tape (D-tape) is a flexible tape measure that displays diameter directly when wrapped around the trunk. Alternatively, use a regular measuring tape and divide by π.

Should I measure above or below a bump or scar?

Always measure at exactly 4.5 feet above ground on the uphill side. If a bump, burl, or scar is present at that height, measure just above or below it and note the deviation.

How many measurements should I take?

For a single measurement point, one circumference reading is sufficient. For research accuracy, measure at two perpendicular angles and average the results to account for non-circular trunks.