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Board Feet Calculator: How to Calculate Lumber
The Formula
Thickness (in) x Width (in) x Length (ft) / 12 = Board Feet
One board foot is a piece of wood 1 inch thick, 12 inches wide, and 1 foot long. It equals 144 cubic inches. Every hardwood lumber transaction in North America uses this unit.
Worked Examples
A 1x12 that’s 8 feet long:
1 x 12 x 8 / 12 = 8 board feet
Straightforward. The width in inches and the length in feet happen to cancel neatly. Now a thicker piece.
A 2x6 that’s 10 feet long:
2 x 6 x 10 / 12 = 10 board feet
And a common rough-sawn hardwood plank, 6/4 stock (1.5” thick), 8 inches wide, 12 feet long:
1.5 x 8 x 12 / 12 = 12 board feet
If you’re buying 40 of those planks for a dining table project’s worth of cherry, that’s 480 board feet. At $7.50/bf for FAS cherry, you’re looking at $3,600 before tax. Board feet make that math possible.
Why Board Feet Exist
Lumber comes in inconsistent widths and lengths. A sawmill doesn’t cut boards to a single size. You might get a 7-inch-wide walnut board that’s 9 feet long sitting next to a 10-inch-wide board that’s 6 feet long. Linear feet can’t price those fairly. Board feet can. The unit captures volume, which is what you’re actually buying.
Softwood lumber (framing, decking, fencing) is sold by the linear foot or by the piece. You buy a 2x4x8 and pay a fixed price for that stick. Nobody at Home Depot quotes you board feet.
Hardwood lumber (oak, maple, walnut, cherry, ash) is sold by the board foot. Always. Walk into any hardwood dealer and the price tag reads $/bf. Same at online suppliers. If you’re building furniture, cabinets, or trim from solid hardwood, you need to speak this language.
Nominal vs Actual Dimensions
This trips people up constantly. A “2x4” from the lumberyard actually measures 1.5 x 3.5 inches. A “1x6” is 0.75 x 5.5 inches. The lumber industry names boards by their rough-sawn dimensions before planing.
For board feet calculations on softwood, use the nominal dimensions. A 2x4 is calculated as 2” x 4”, not 1.5” x 3.5”. That’s the convention.
For hardwood, it depends on how you’re buying. Rough-sawn lumber from a mill uses actual thickness. Hardwood thickness follows the “quarter” system:
| Quarter Name | Rough Thickness | Surfaced (S2S) |
|---|---|---|
| 4/4 | 1” | 13/16” |
| 5/4 | 1-1/4” | 1-1/16” |
| 6/4 | 1-1/2” | 1-5/16” |
| 8/4 | 2” | 1-3/4” |
| 10/4 | 2-1/2” | 2-1/4” |
| 12/4 | 3” | 2-3/4” |
When you buy 8/4 walnut, you use 2” as the thickness for your board feet calculation, even though surfaced stock will be 1-3/4”. You’re paying for the rough-sawn volume.
Board Feet Reference Table
Common softwood lumber, per piece:
| Size | 8 ft | 10 ft | 12 ft | 14 ft | 16 ft |
|---|---|---|---|---|---|
| 1x4 | 2.67 | 3.33 | 4.0 | 4.67 | 5.33 |
| 1x6 | 4.0 | 5.0 | 6.0 | 7.0 | 8.0 |
| 1x8 | 5.33 | 6.67 | 8.0 | 9.33 | 10.67 |
| 1x12 | 8.0 | 10.0 | 12.0 | 14.0 | 16.0 |
| 2x4 | 5.33 | 6.67 | 8.0 | 9.33 | 10.67 |
| 2x6 | 8.0 | 10.0 | 12.0 | 14.0 | 16.0 |
| 2x8 | 10.67 | 13.33 | 16.0 | 18.67 | 21.33 |
| 2x10 | 13.33 | 16.67 | 20.0 | 23.33 | 26.67 |
| 2x12 | 16.0 | 20.0 | 24.0 | 28.0 | 32.0 |
| 4x4 | 10.67 | 13.33 | 16.0 | 18.67 | 21.33 |
These use nominal dimensions. Pin this table to your shop wall or screenshot it. You’ll reference it more than you think.
Board Feet vs Linear Feet
Linear feet measures length only. Board feet measures volume. They answer different questions.
Use linear feet when buying dimensional lumber at fixed sizes. Framing a wall? Count your studs by the piece. Installing deck boards? Price per linear foot. The cross-section is already defined by the product.
Use board feet when buying lumber that varies in width and thickness. Picking through a stack of rough walnut at the hardwood dealer, each board is a different size. Board feet is the only honest way to price them.
One quick conversion that comes up at the lumberyard: if someone quotes you a per-linear-foot price on dimensional lumber and you want to compare it to a board foot price, convert the stick to board feet and divide.
Example: a 2x6x12 sells for $8.40 at the home center. That’s 12 board feet. $8.40 / 12 = $0.70 per board foot. Not bad for SPF.
Waste and Yield
Raw board feet and finished board feet are different numbers. If you’re buying rough hardwood to mill into furniture parts, you’ll lose material to:
- Planing both faces (takes off 3/16” total, sometimes more)
- Jointing one edge
- Crosscutting around defects, checks, and knots
- Ripping to final width
A common rule of thumb is 20-25% waste for furniture work. If your cut list calls for 80 board feet of finished parts, buy 100. Really knotty or lower-grade stock? Go 30%. Premium FAS grade with long, clear boards? You might get away with 15%.
This is where the money math matters. Buying S2S (surfaced two sides) stock saves milling time but costs more per board foot and still gives you less volume than the nominal thickness suggests.
When the Math Gets Stacked
Lumber orders add up fast. Say you’re building kitchen cabinets. The face frames need 30 bf of hard maple. Drawer boxes need 20 bf of poplar. Drawer fronts and door panels need 45 bf of cherry. Plus the concrete for your shop pad if you’re starting from scratch.
That’s 95 bf before waste factor. With 20% added, you’re ordering 114 bf across three species at three different price points. Each species comes in random widths, random lengths. Getting the cost right means getting the board feet right.
It’s easy to mess up when you’re standing in the lumber aisle with a phone calculator and sawdust in your eyes. The formula is simple. Running it 50 times for a materials list is tedious.
Running the Numbers Faster
SiteCalc has a board feet calculator that handles singles and full material lists. Punch in thickness, width, and length, and it gives you board feet, total cost at your price per bf, and waste-adjusted quantities. The show formula feature breaks down every calculation so you can double-check the math yourself. Faster than a tape measure and a stubby pencil at the hardwood dealer.