Board Feet Calculator
Board feet from any lumber size, with quarter-system support.
How to use
Type the lumber dimensions and quantity. Optional: enter a per-board-foot price to see total cost. Updates as you type.
- Enter thickness in inches or quarter notation (4/4 = 1″, 5/4 = 1.25″, 8/4 = 2″).
- Enter width in inches.
- Enter length in feet.
- Enter quantity. Optionally enter a price per board foot for a total cost.
Reviewed 3 June 2026 · methodology cited
About this calculator
A board foot is the volume of a piece of lumber that is one inch thick, twelve inches wide, and one foot long — 144 cubic inches in total. Hardwood is almost always sold by the board foot in North America (sometimes by the linear foot for dressed mouldings), and softwood is sold either by the linear foot or the board foot depending on the species and grade. Pricing per board foot lets you compare different sizes apples-to-apples; pricing per linear foot does not.
This calculator takes the four numbers a yard or mill asks for — thickness, width, length, and quantity — and returns the board feet for one piece, the total for the order, and (if you fill in a price) the total cost. It accepts thickness in either decimal inches or the quarter system used in hardwood (4/4 means four quarters of an inch = 1″; 5/4 = 1.25″; 8/4 = 2″) so you can type exactly what the mill quoted.
The math behind it
Board feet for one piece is calculated as: BF = (T × W × L) ÷ 12 — where T is thickness in inches, W is width in inches, and L is length in feet. The 12 in the denominator converts square inches × feet to the 144-cubic-inch board-foot unit. For multiple identical pieces, multiply by the quantity. The price field, when filled, multiplies the total board feet by the per-board-foot rate.
A worked example: ten 8/4 oak boards, 6 inches wide and 8 feet long, at $9 per BF. Each piece is (2 × 6 × 8) ÷ 12 = 8 BF. Ten pieces = 80 BF. Cost = 80 × $9 = $720. Always confirm the actual dimensions with the mill — rough lumber is closer to nominal, dressed lumber loses about 1/4″ per side in planing.
Common lumber sizes
| Thickness | Actual (dressed) | Common use |
|---|---|---|
| 4/4 | 13/16″ | Boards, paneling, cabinet faces |
| 5/4 | 1 1/16″ | Treads, stair caps, heavy shelving |
| 6/4 | 1 5/16″ | Door jambs, beam ledgers |
| 8/4 | 1 13/16″ | Mantles, table tops, structural |
| 10/4 | 2 3/8″ | Heavy table tops, posts |
| 12/4 | 2 7/8″ | Beams, turning blanks |
| 16/4 | 3 7/8″ | Large beams, custom posts |
Tips for ordering and stacking
Order in board feet for hardwood and in linear feet for trim. Yards quote rough lumber by nominal thickness (4/4, 5/4, 8/4) but dressed lumber loses about 1/4″ per face when planed, so a 4/4 dressed board is closer to 13/16″, not a full inch. Calculate board feet from the nominal thickness — the yard prices that way.
Add waste for cut-off and defects. Furniture-grade hardwood typically needs 10–20 percent extra; cabinet stock 15–25 percent if you are working around a specific colour or figure. Rough construction lumber is often 5–10 percent. Stack lumber flat with stickers between layers if you are storing it for more than a few days — even kiln-dried boards will move if they sit on a damp floor or against a wall.
Frequently asked questions
What is a board foot?
A board foot is 144 cubic inches of lumber — one inch thick, twelve inches wide, and one foot long. It is a volume unit, not a length unit, so two pieces of different dimensions can equal the same board feet. A 1×6×8 ft board (4 BF) holds the same volume as a 1×12×4 ft board (4 BF).
What does 4/4, 5/4, 8/4 mean?
The quarter system measures hardwood thickness in quarter inches. 4/4 (read "four-quarter") is four quarters of an inch — one inch. 5/4 is 1.25″, 6/4 is 1.5″, 8/4 is 2″. These are nominal (rough) thicknesses; once dressed (planed), each face loses about 1/8″ to 1/4″ — so 4/4 dressed is typically 13/16″.
Should I use nominal or actual thickness for the calculation?
Use nominal thickness when calculating board feet for ordering — that is how the yard prices the lumber. Use actual (dressed) thickness when working out finished dimensions for a build. The board feet you pay for is computed from the nominal size before planing.
Why is length in feet and width in inches?
It mirrors how mills measure and price lumber — boards are graded and stacked by length in feet, but cut and edged to width in inches. The division by 12 in the formula reconciles the units. Some calculators ask for length in inches; the math is the same with a division by 144 instead of 12.
How much waste should I add?
For furniture-grade hardwood, plan 10–20 percent extra. For colour or figure matching, plan 15–25 percent. For rough framing lumber, 5–10 percent. Add more if you are working with short scraps or need long clear runs. The lumber yard will not return opened bundles, so it is cheaper to overbuy a little than to make a second trip.
Is this for finishing or rough lumber decisions?
Reference utility only. Use the result for ordering and budgeting; verify finished dimensions against your actual stock before cutting. Structural sizing and grade selection belong to a building plan reviewed by a qualified contractor or engineer.