Board Foot Calculator
Find the board footage of hardwood or rough lumber from its thickness, width and length. Choose a standard quarter-size (4/4 through 12/4) or enter custom dimensions, set a quantity and waste allowance, and get the total board feet to order. Add a price per board foot for a full cost estimate.
Formula
Worked example
Ten 4/4 (1 in) boards, 6 in wide and 8 ft long: each is (1 × 6 × 8) / 12 = 4 BF, so 10 boards = 40 BF net. Adding a 10% waste allowance gives 44 BF to order. At $5.50/BF, total cost = 44 × 5.50 = $242.
What a board foot measures
A board foot is a unit of volume used to price rough and hardwood lumber: one board foot is exactly 144 cubic inches, the volume of a piece one inch thick, twelve inches wide and twelve inches long. Because lumber is sold by how much wood it contains, two boards with different shapes can have the same board footage. A 1×12 board that is one foot long and a 2×6 board that is one foot long both equal exactly one board foot, since each holds 144 cubic inches of material. The board foot is the standard pricing unit at hardwood dealers and sawmills across North America.
How the formula works and why you divide by 12
The trade formula multiplies thickness in inches by width in inches by length in feet, then divides by 12. If you measured every dimension in inches you would divide by 144 to get cubic inches per board foot. Keeping length in feet already factors in one multiple of 12 (since 1 foot equals 12 inches), so you only divide by the remaining 12. Both approaches give the same answer. The calculator applies thickness and width in inches and length in feet, which matches how lumber yards quote stock, then multiplies by quantity and applies your waste allowance.
Quarter-sizes, nominal dimensions and NHLA rounding
Hardwood thickness is quoted in quarters of an inch of rough stock. 4/4 means four quarters, or one inch; 6/4 is one and a half inches; 8/4 is two inches; 12/4 is three inches. These are nominal rough thicknesses measured before the board is planed, so the finished dressed piece will be slightly thinner. Under National Hardwood Lumber Association (NHLA) rules, lumber thinner than 4/4 is priced as if it were 4/4, and thickness is rounded up to the next quarter-inch. Use nominal rough dimensions when calculating board feet, never the surfaced size.
Waste allowance, pricing and ordering tips
Rough lumber almost always contains some unusable material: knots, splits, wane, checking at the ends and the offcuts created when you rip and crosscut boards to finished size. Adding a waste allowance of 10-15% is standard practice for clear or FAS-grade hardwood; go up to 20-25% for knotty or short boards. The calculator multiplies the net board footage by your chosen waste percentage before showing the order quantity, so you can immediately see how much stock to buy. When pricing, your supplier quotes a per-board-foot rate based on species, grade and thickness; multiply that rate by the waste-adjusted total to get the order cost.
Using metric dimensions
If you are sourcing timber in metric countries, switch the unit system to metric and enter all three dimensions in centimetres. The calculator converts to inches and feet internally before applying the standard trade formula, so the board footage result is the same as if you had measured in imperial. Lumber sold in metric markets is sometimes priced per cubic metre instead of per board foot; in that case, note that one board foot equals 2,359.74 cubic centimetres, so 1,000 BF equals about 2.36 cubic metres.
Board feet for common nominal sizes (per board per foot of length)
| Nominal size | Quarter-size | BF per lineal foot | BF for 8 ft board | BF for 10 ft board | BF for 12 ft board |
|---|---|---|---|---|---|
| 1 × 4 | 4/4 | 0.33 | 2.67 | 3.33 | 4.00 |
| 1 × 6 | 4/4 | 0.50 | 4.00 | 5.00 | 6.00 |
| 1 × 8 | 4/4 | 0.67 | 5.33 | 6.67 | 8.00 |
| 1 × 10 | 4/4 | 0.83 | 6.67 | 8.33 | 10.00 |
| 1 × 12 | 4/4 | 1.00 | 8.00 | 10.00 | 12.00 |
| 1.5 × 6 | 6/4 | 0.75 | 6.00 | 7.50 | 9.00 |
| 2 × 4 | 8/4 | 0.67 | 5.33 | 6.67 | 8.00 |
| 2 × 6 | 8/4 | 1.00 | 8.00 | 10.00 | 12.00 |
| 2 × 8 | 8/4 | 1.33 | 10.67 | 13.33 | 16.00 |
| 3 × 6 | 12/4 | 1.50 | 12.00 | 15.00 | 18.00 |
BF per linear foot = (T_in × W_in) / 12. Multiply by your board length to get board feet per board.
Frequently asked questions
Why divide by 12 and not 144?
A board foot is 144 cubic inches. If every dimension is in inches you divide by 144. The standard lumber trade formula keeps length in feet rather than inches, which already accounts for one factor of 12 (since 1 foot is 12 inches), so you only divide by the remaining 12. Both methods give the same answer as long as units are consistent.
What do 4/4, 6/4, 8/4 and 12/4 mean?
These are NHLA quarter-size codes for rough hardwood thickness. Each number is the thickness in quarters of an inch: 4/4 is one inch, 6/4 is one and a half inches, 8/4 is two inches, and 12/4 is three inches. These are nominal rough thicknesses before planing, so the dressed board will be slightly thinner. The calculator has a preset dropdown for all common quarter-sizes so you do not have to remember the decimal equivalents.
Should I use nominal or actual (dressed) dimensions?
Use nominal (rough) dimensions, because board footage is calculated and priced on the rough size before surfacing. A board sold as 1 inch by 6 inches is measured at exactly those dimensions even though the dressed board is smaller after planing. Using dressed dimensions would under-count the wood you are paying for.
How much waste should I add?
For clear or FAS-grade hardwood with few defects, a 10-15% waste allowance is typical. Add 20-25% for boards with knots, checks or wane, or when you are cutting many short pieces and expect a lot of end-grain loss. The waste field in this calculator defaults to 10% and applies it to the net board footage to give you a ready-to-order figure.
How do I calculate board feet for a log (using the Doyle rule)?
The Doyle log rule estimates board feet from a standing tree or log using the formula: BF = ((diameter_in_inches - 4) / 4)^2 × length_in_feet. It is commonly used by sawmills in the eastern United States but tends to under-estimate small logs. This calculator is for sawn boards; use a dedicated log-scale calculator for timber cruising.
What is the difference between board feet and linear feet?
A linear foot is a one-dimensional measure of length only: a 10-foot board is 10 linear feet regardless of thickness or width. A board foot is a three-dimensional volume measure. A 1×6 board that is 10 feet long is 5 board feet, while a 2×6 that is 10 feet long is 10 board feet, even though both are 10 linear feet. Board feet account for how much wood you are actually buying.