Board Foot Calculator
A board foot is 144 cubic inches of rough lumber — one foot long, one foot wide, one inch thick. To calculate board feet, multiply thickness (in) × width (in) × length (in) and divide by 144, then multiply by the number of boards. The calculator below handles quarter-system thicknesses (4/4, 5/4, 6/4, 8/4), lengths in feet or inches, and an optional price per board foot.
Worked example
Say you're buying an 8-foot white oak board, 6 inches wide, in 4/4 (1 inch) thickness. Convert the length to inches (8 × 12 = 96), then:
96 × 6 × 1 ÷ 144 = 4.0 board feet
At $6.50 per board foot, that board costs 4.0 × 6.50 = $26.00. Ten of them would be 40 board feet — $260.
What a board foot actually measures
A board foot is the standard volume unit for hardwood lumber in North America: 144 cubic inches, pictured as a board one foot long, one foot wide, and one inch thick. Lumber is sold by volume rather than by length because boards come in wildly different widths and thicknesses — a price per board foot lets a dealer price an 11-inch-wide slab of 8/4 walnut and a narrow 4/4 poplar stick on the same scale.
The tricky part is which dimensions to plug in. Hardwood is tallied in the rough: a 4/4 board is counted as a full 1 inch thick even though it will surface out near 13/16 inch, and width is measured before edges are straightened. Softwood construction lumber goes further and uses nominal sizes — a 2×4's board footage is figured at 2 by 4 inches even though it actually measures 1.5 by 3.5 inches. Neither convention is cheating; it's how the industry accounts for the wood the mill started with before drying, planing, and edging removed some of it.
Two practical tips. First, measure width at the narrowest usable point of a waney or tapered board — you can't build with bark. Second, board footage is a purchasing measure, not a yield measure: once you cut around knots, checks, and sapwood and joint everything square, expect to keep 70–85% of what you bought. Price your projects on delivered board feet plus that waste factor, and the lumber bill stops surprising you.
Frequently asked questions
- How many board feet are in a 2×4 that is 8 feet long?
- Using nominal dimensions, a 2×4×8′ is 2 × 4 × 96 ÷ 144 = 5.33 board feet. Board footage for dimensional lumber is conventionally figured on nominal size, even though the actual surfaced size is 1.5″ × 3.5″. Hardwood dealers work from actual rough dimensions instead.
- What does 4/4, 5/4, or 8/4 lumber mean?
- Hardwood thickness is quoted in quarters of an inch, measured in the rough: 4/4 ("four-quarter") is 1″ thick, 5/4 is 1.25″, 6/4 is 1.5″, and 8/4 is 2″. After drying and surfacing, a 4/4 board typically finishes around 13/16″, but you are charged on the rough quarter size.
- Is a board foot the same as a linear foot?
- No. A linear foot measures length only, ignoring width and thickness. A board foot is a volume unit — 144 cubic inches. An 8-foot board is always 8 linear feet, but it could be 4 board feet (4/4 × 6″) or 16 board feet (8/4 × 12″).
- Should I measure rough or surfaced dimensions?
- Use the rough (pre-surfacing) dimensions — that is what sawmills and hardwood dealers charge on. If you only have surfaced stock to measure, remember the seller's tally was taken before planing, so your measured volume will come out slightly under what you paid for.
- How much extra should I buy for waste?
- Most woodworkers add 15–30% over the calculated board footage. Defects, checked ends, planing losses, and grain matching all consume stock; complex projects with many show surfaces sit at the high end of that range.