Calculate tree diameter at breast height (DBH) from circumference and determine basal area using the standard forestry measurement method.
Last updated: March 2026
DBH (Diameter at Breast Height) is the standard forestry measurement of tree size, recorded as diameter measured at 4.5 feet (1.37 meters) above ground level. This universal standard allows foresters, arborists, and scientists to compare tree sizes consistently across different regions and time periods.
DBH is critical for estimating tree volume, biomass, age, carbon storage, and biodiversity value. Basal area (cross-sectional area of the tree trunk calculated from DBH) is used to determine forest density and timber yield. In urban forestry, DBH directly correlates to canopy size, shade provision, and ecosystem services.
Circumference-to-diameter conversion is straightforward: DBH = Circumference ÷ π (3.14159). This relationship is fundamental to all forestry calculations and is sometimes called "DBH conversion" or "girth measurement" when working with raw circumference data collected in the field.
Basal area is the cross-sectional area of the tree trunk at DBH. Formula: A = π × r² where r = DBH ÷ 2
Calculate DBH from a circumference of 56.5 inches:
4.5 feet (1.37 m) is the international forestry standard to ensure consistency. It's above typical understory shrubs and below the lowest branches on most trees, providing a stable, repeatable measurement height.
Yes, DBH works for most trees. For trees with multiple trunks below 4.5 feet, measure each stem separately. For leaning trees, measure perpendicular to the stem. Severely twisted or forked trees may require special handling.
DBH is specifically the diameter at 4.5 feet above ground—the standard forestry measurement. 'Diameter' can refer to any cross-section. DBH allows universal comparison across different species and regions.
Yes. If you have basal area, solve for diameter: DBH = 2 × √(Basal Area ÷ π). For example, 1.77 sq ft = 2 × √(1.77 ÷ π) = ~18 inches.
Total basal area (TBA) is the sum of basal areas for all trees in an acre. Healthy forests have TBA of 80–120 sq ft/acre. Below 30 sq ft/acre indicates overharvesting; above 200 indicates overcrowding.
Age can be estimated using growth rates: Age ≈ DBH ÷ growth rate. For example, a tree growing 0.5″ per year with DBH of 18″ is roughly 36 years old. Use the Tree Age Calculator for more precise estimates.
Related Tools