Board Foot Calculator — Lumber Purchases

A board foot (BF) is a unit of volume equal to a 1-inch thick board that is 12 inches wide and 1 foot long (144 cubic inches). It is the standard unit for pricing hardwood lumber. The formula is: thickness (inches) x width (inches) x length (feet) / 12.

4/4 means four-quarter, or 1 inch thick when rough-sawn. 5/4 is 1.25 inches, 6/4 is 1.5 inches, 8/4 is 2 inches, and 12/4 is 3 inches. After planing, the finished thickness is typically 1/8 to 3/16 inch less than the rough size.

Allow 15-20% waste for typical projects. This accounts for defects (knots, splits, sapwood), saw kerf, planing, and off-cuts. For clear, high-grade lumber, 10-15% may suffice. For lower grades with more defects, allow 20-25%.

When you surface (plane) rough lumber you lose thickness. Under the NHLA standard surfacing allowance a 4/4 (1") board finishes to 13/16" (0.8125") and 8/4 (2") finishes to 1-3/4" (1.75"). The calculator's default ratio of 0.85 models a lighter clean-up skim (4/4 → 0.85", 8/4 → 1.70"); lower it towards 0.81 if you want the full NHLA S2S finished thickness.