How to calculate board feet

A board foot is lumber volume, not length: one board foot is a piece 1 inch thick by 12 inches wide by 12 inches long — 144 cubic inches. Hardwood is priced by it because rough boards come in random widths and lengths, so volume is the only fair meter. The formula:

BF = thickness (in) × width (in) × length (ft) / 12

or, with every dimension in inches, divide by 144 instead. The board feet calculator runs this per board, multiplies by quantity, adds your waste allowance and prices the total.

The quarter system

Hardwood thickness is named in quarters of an inch of rough thickness:

4/4 = 1 in  ·  5/4 = 1¼ in  ·  6/4 = 1½ in  ·  8/4 = 2 in

Two conventions follow. First, board feet are computed from that rough thickness even after surfacing — a planed 4/4 board measuring 13/16 in still tallies as 1 in stock. Second, anything under 4/4 counts as 4/4 for pricing at most yards. Width is measured as-is (random width is normal in hardwood); length usually rounds down to the foot.

Worked example — pricing a small order

An 8/4 maple board, 6 in wide and 10 ft long:

BF = 2 × 6 × 10 / 12 = 10 board feet

At $6.50 per board foot that is $65 for the board. A project needing 24 BF net of parts, bought with a 25% waste allowance, means purchasing 24 × 1.25 = 30 BF — three such boards, $195. That allowance is not pessimism: kerf, end checks, knots and milling from 2 in rough to 1¾ in finished all come out of the same volume.

Board feet vs linear feet vs square feet

• Linear feet price length only — used for moldings and dimensional softwood where the cross-section is fixed.
• Square feet price area — sheet goods like plywood (a 4×8 sheet is 32 sq ft, the basis of the plywood calculator).
• Board feet price volume — rough hardwood. Converting: a 4/4 board has 1 BF per square foot of face; an 8/4 board has 2.

For the rest of the buying workflow: the cut list calculator converts part lists into stock-board purchases, the lumber weight calculator turns the volume into payload by species, and the wood movement calculator screens the moisture-driven width change before you commit the freshly bought stock to a glue-up.

Frequently asked questions

What is the board foot formula?

BF = thickness (in) × width (in) × length (ft) / 12 — or with all three dimensions in inches, divide by 144. One board foot is the volume of a 1 in × 12 in × 12 in piece: 144 cubic inches.

Do I use nominal or actual dimensions for board feet?

For rough hardwood lumber, board feet are tallied from the rough (nominal) thickness — a surfaced 4/4 board that now measures 13/16 in still sells as 1 in stock. Width is measured as-is on random-width hardwood. Softwood dimensional lumber (2×4s) is usually sold by the piece, not by board foot.

What does 4/4, 5/4, 8/4 lumber mean?

Hardwood thickness is quoted in quarters of an inch: 4/4 = 1 in, 5/4 = 1.25 in, 6/4 = 1.5 in, 8/4 = 2 in rough thickness. The quarter system names the rough-sawn thickness before surfacing, which is also the thickness used for board-foot pricing.

How much waste should I add when buying lumber?

A common allowance is 15–30% over the net part volume: kerf, end checks, knots, color and grain matching, and milling to final thickness all consume stock. Figured or rustic grades and small parts push the allowance higher.