Enter your tree's circumference (and your unit of measurement) into the Tree Diameter Calculator to find its Diameter at Breast Height (DBH) — the standard measure foresters use to classify tree size. Got a multi-stemmed tree? Add your additional stem circumferences to get a combined DBH and see which tree size category your tree falls into.
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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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.
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.
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.
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.
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.
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.
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.
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.