Tree Diameter Calculator

The Tree Diameter Calculator converts a tree's trunk measurement into its Diameter at Breast Height (DBH) — a standard forestry metric measured at 4.5 feet (1.37m) above ground, used in tree surveys, timber assessments, and urban tree management. Enter your Tree Circumference (or direct diameter), select your Unit of Measurement, and choose your Measurement Type to get the DBH along with its value in alternative units and a Tree Size Category. For trees with multiple trunks, check Multi-stem Tree and enter your Additional Stem Circumferences to get a Combined DBH.

Measure at 4.5 feet (1.37m) above ground level

Circumference measurement is more accurate for irregular trunks

Check if tree has multiple trunks/stems

For multi-stem trees, enter other stem circumferences

Results

Diameter at Breast Height (DBH)

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DBH in Alternative Units

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Combined DBH (Multi-stem)

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Tree Size Category

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Frequently Asked Questions

How do you find the diameter of the wood inside the bark?

To find the diameter inside the bark, you need to subtract twice the bark thickness from the total DBH. Bark thickness varies by species but typically ranges from 0.5-2 inches for mature trees.

How do I calculate the diameter of a tree on a slope?

On sloped ground, measure DBH on the uphill side of the tree at 4.5 feet above the natural ground line. This ensures consistent measurement standards regardless of terrain.

How do I measure the circumference of a leaning tree on level ground?

For leaning trees, measure the circumference at 4.5 feet along the trunk from the base, not 4.5 feet vertically. Follow the trunk's natural curve to maintain the standard measurement point.

How do I calculate the diameter of a multi-stemmed tree?

For multi-stemmed trees, measure each stem individually at breast height. Calculate each diameter separately, then use the formula: Combined DBH = √(D1² + D2² + D3² + ...) where D represents each stem's diameter.

How do I measure the diameter of a tree stump?

For tree stumps, measure the diameter directly across the stump face at its widest point. If the stump is irregular, take multiple measurements and average them for accuracy.

How much does a tree grow in diameter per year?

Tree diameter growth varies by species, age, and conditions. Young trees may grow 0.5-1 inch per year, while mature trees typically grow 0.1-0.25 inches annually. Fast-growing species like poplars can exceed these rates.

How do I calculate my 10 year-old oak tree's circumference without a tape?

You can estimate circumference using a string or rope wrapped around the trunk, then measure the string length with a ruler. Alternatively, use your arm span (typically 5-6 feet for adults) as a rough measuring guide.

How do I calculate the diameter of a tree of circumference 40 cm?

To calculate diameter from circumference, divide by π (3.14159). For a 40 cm circumference: Diameter = 40 ÷ 3.14159 = 12.73 cm. This is the basic formula: D = C ÷ π.