BA = π/4 × DBH² (per tree) or BA/acre for stands
Basal area (BA) is the cross-sectional area of a tree trunk at breast height (4.5 ft / 1.37 m). It is calculated as BA = π/4 × DBH². For a stand, total BA per acre indicates stocking density: open pine forests 60-80 ft²/ac, fully stocked hardwoods 100-150 ft²/ac. Basal area is the most important forestry metric for timber volume estimation, thinning prescriptions, and wildlife habitat assessment. It is measured with prism cruising or angle gauge sampling in the field. Stand basal area combined with site index and species determines growth rate and harvest timing.