Rough and hardwood lumber is priced by the board foot, not by the piece, and the board foot trips people up because it mixes inches and feet in one number. One board foot is 144 cubic inches of wood: a piece one inch thick, twelve inches wide, and one foot long. This board foot calculator does the conversion for you. Enter the nominal thickness and width in inches, the length in feet, and how many boards you are buying, and it returns total board feet. Add a price per board foot and it returns the material cost. Use nominal dimensions the way the yard quotes them, and remember that four-quarter, five-quarter, and thicker stock is measured by its rough thickness, not the surfaced dimension.
Board Foot Calculator: Lumber Volume and Cost
Calculate board feet from thickness, width, length, and quantity, and get material cost from a price per board foot. Built for hardwood and rough lumber estimating.
Board Foot Calculator
Enter the nominal thickness and width in inches, the length in feet, and how many boards. Add a price per board foot for a material cost.
Board feet40.0 bd ft
Estimates for planning only. Check the result against your plans and a supplier quote before you order.
How to Use the Calculator
Enter thickness in inches. Rough lumber is sold in quarters, so four-quarter stock is one inch, five-quarter is one and a quarter, and eight-quarter is two inches. Use the rough thickness the yard prices from, not the planed dimension. Enter width in inches and length in feet. Then enter the number of boards at those dimensions. If your boards vary, run the calculator once per size and add the totals. Finally, enter a price per board foot if you want a cost, and the calculator multiplies board feet by price. Leave the price at zero to get board feet only.
The Formula
Board feet equal thickness in inches times width in inches times length in feet, divided by twelve, times the number of boards. The divide-by-twelve is the part people forget: it converts the inch-inch-foot mix into the 144-cubic-inch board foot. A one-by-six that is eight feet long is one times six times eight divided by twelve, or four board feet. Ten of them is forty board feet. At three dollars a board foot, that is one hundred twenty dollars of lumber before waste.
Nominal Versus Actual
Board feet are figured from nominal dimensions, the size the board is called, not the surfaced size you measure with a tape. A one-by-six is really about three quarters by five and a half inches after surfacing, but it is sold and priced as a one-by-six. Enter the nominal numbers. The exception is rough-sawn stock that has not been surfaced, where the nominal and actual are close. When in doubt, use the dimension the supplier quotes on the invoice, because that is the number they billed from.
Add for Waste
The calculator gives you the board feet in the boards themselves. It does not add cutting waste, defect, or the offcuts that never make it into the work. For furniture-grade hardwood with knots and checks to cut around, plan on ordering fifteen to thirty percent over your finished board-foot count. For clean, straight rough lumber going into framing or shelving, ten to fifteen percent is usually enough. Order to the higher number so a bad board or a miscut does not send you back to the yard mid-project.
When Not to Use Board Feet
Not all lumber is priced by the board foot. Dimensional softwood at a home center, like a two-by-four stud, is usually sold by the piece or by the linear foot, so board-foot math is the wrong tool there. Sheet goods like plywood are sold by the sheet or square foot. Board feet are for lumber priced by volume, which in practice means hardwood, rough-sawn stock, and thicker specialty lumber. If the price tag reads per piece or per linear foot, price it that way instead.
Board Foot Reference
| Reference | Planning value | Field note |
|---|---|---|
| One board foot | 144 cubic inches | 1 in thick x 12 in wide x 1 ft long |
| 1x6 x 8 ft | 4 board feet | 1 x 6 x 8 / 12 |
| Quarter system | 4/4 = 1 in, 8/4 = 2 in | Rough thickness the yard prices from |
| Use nominal | Called size, not surfaced | A 1x6 is priced as a 1x6 |
| Add waste | 10-30% over finished | Higher for defect-heavy hardwood |
FAQ
How do you calculate board feet? Multiply thickness in inches by width in inches by length in feet, then divide by twelve, then multiply by the number of boards. A one-by-six that is eight feet long is four board feet.
What is a board foot? One board foot is 144 cubic inches of wood, the amount in a piece one inch thick, twelve inches wide, and one foot long. It is a volume measure, which is why hardwood and rough lumber are priced by it.
Do I use nominal or actual dimensions? Use nominal dimensions, the size the board is called and sold as, not the smaller surfaced size you measure. Price a one-by-six as a one-by-six. Match whatever the supplier quotes on the invoice.
Should I add waste to the board-foot total? Yes. The calculator counts the wood in the boards, not cutting waste or defect. Add roughly ten to fifteen percent for clean lumber and fifteen to thirty percent for defect-heavy hardwood you have to cut around.