📚 What's in This Guide
This board foot calculator finds the volume of lumber in board feet and shows what it will cost. Add as many boards as you need, type thickness and width as decimals or fractions, enter lengths in feet and inches, and the total updates as you go. If you searched for a board feet calculator, a bd ft calculator, a board footage calculator, or a boardfoot calculator, this is the same tool. It also converts board feet to square feet and cubic units, and scales logs with three standard log rules.
Below you will find the formula, the difference between nominal, rough, and surfaced sizes, worked examples, reference charts, and the log formulas.
Board feet = thickness (in) × width (in) × length (ft) ÷ 12. A board 1 in thick, 8 in wide, and 8 ft long is 5.33 board feet.
1. What Is a Board Foot?
A board foot is a unit of volume used to buy and sell lumber. One board foot is the amount of wood in a board 1 foot long, 1 foot wide, and 1 inch thick, which is 144 cubic inches or one twelfth of a cubic foot. The unit is written BF, BDFT, or FBM (foot, board measure), and 1,000 board feet is written MBF.
It exists because boards differ in thickness and width, so length alone does not tell you how much wood you are buying. A board 1 in thick, 4 in wide, and 8 ft long holds the same wood as one that is 1 in thick, 8 in wide, and 4 ft long, and the board foot shows that they are equal. Hardwood, rough-sawn lumber, and slabs are usually priced this way, while framing lumber is mostly sold by the piece.
2. How the Board Foot Calculator Works
The calculator has three tools, which you switch between with the tabs.
Lumber list. Each board has a quantity, a thickness, a width, and a length. You can pick a quick size, either a hardwood thickness in quarters (4/4 to 16/4) or a nominal dimensional size such as 2 x 4, and the thickness and width fill in. Thickness and width accept decimals and fractions, such as 1.25, 3/4, or 8 1/4. Length has two boxes, feet and inches. The calculator works out the board feet of each board, multiplies by its quantity, and adds them all up. You can add up to 15 boards.
Convert. This changes board feet to square feet and back for a given thickness, and converts between board feet, MBF, cubic feet, cubic inches, cubic meters, and liters.
Log. Enter the small-end diameter inside the bark, the length, and the number of logs, and the calculator shows the board feet by the Doyle, Scribner, and International 1/4 inch rules side by side.
In the lumber list you also get cubic feet, cubic meters, MBF, the number of pieces, and total length, plus optional waste, price, and cost. A breakdown table shows every board, and a step-by-step block shows the math.
The lumber list uses the exact formula with the thickness and width you enter. It does not apply any dealer's tally rules, such as rounding or dropping fractions of a foot. Log results are estimates, since log rules are formulas, not measurements of the lumber you will actually get. Confirm quantities with your supplier before you order.
3. How to Use the Board Foot Calculator
- Choose imperial units (inches and feet) or metric units. In metric, thickness and width are in millimeters and length is in meters and centimeters.
- Pick a quick size, or choose Custom and type the thickness and width yourself. Fractions such as 3/4 and 1 1/2 are accepted.
- Enter the length in feet and inches. Leave the inches box empty if it is zero.
- Set the quantity if you need several boards of the same size.
- Use Add Another Board for each different size on your list, up to 15.
- Optionally enter a waste percentage and a price per board foot.
- Read the total board feet, the other units, the breakdown table, and the step-by-step math.
- Use the Convert tab for square feet and cubic units, and the Log tab for logs.
- Use Copy Result, Share Result, or Download PDF for the tool you are on, and Reset All to start again.
If a board is missing a measurement, has an unreadable fraction, or has a quantity that is not a whole number, the calculator tells you which board needs attention and leaves it out until you fix it.
4. Board Foot Formula and How to Calculate It
There are two forms of the formula. They give the same answer and differ only in the unit of length.
Board feet = thickness (in) x width (in) x length (ft) / 12
Board feet = thickness (in) x width (in) x length (in) / 144
Multiply by the number of boards to get the total for a quantity.
To measure board feet by hand, follow these steps.
- Measure the thickness of the board in inches. For hardwood, use its quarter designation, such as 4/4 for 1 inch.
- Measure the width across the face in inches. For boards with uneven edges, measure at the narrow point or take an average.
- Measure the length in feet.
- Multiply the three numbers and divide by 12.
- For a stack of different boards, repeat for each size and add the results.
To estimate board feet before you buy, work out the size of every part in your plan, calculate each part, add them up, and then add an allowance for waste.
5. Nominal, Rough, and Surfaced Sizes
This is where most mistakes happen. Lumber has a size it is sold as and a size you can measure, and board feet usually use the first one.
Hardwood. Thickness is given in quarters of an inch, a system set by the National Hardwood Lumber Association (NHLA). The quarter number refers to the rough thickness. When a board is planed smooth, it gets thinner, but it is still counted at its rough thickness. A 4/4 board is counted as 1 inch even when it is surfaced to about 13/16 inch.
| Quarters | Rough thickness | Typical surfaced two sides (S2S) |
|---|---|---|
| 4/4 | 1 in | 13/16 in |
| 5/4 | 1 1/4 in | 1 1/16 in |
| 6/4 | 1 1/2 in | 1 5/16 in |
| 8/4 | 2 in | 1 13/16 in |
| 12/4 | 3 in | 2 13/16 in |
If you buy surfaced hardwood and calculate with its measured thickness instead of its quarter size, you will come out about 19 percent low on 4/4 stock (13/16 is 0.8125, compared with 1). Rough boards can also vary a little from their nominal thickness, so measure if it matters.
Softwood framing. A 2 x 4 is called that because of its nominal size before drying and planing. It actually measures about 1.5 by 3.5 inches. In the softwood trade, board feet are normally figured from the nominal width and thickness and the actual length, so a 2 x 4 x 8 counts as 2 x 4 x 8 / 12 = 5.33 board feet, not the 3.5 board feet of wood in the piece. Because of this, the quick sizes for dimensional lumber use nominal values.
The practical rule is to use the size the seller uses for pricing. If you are checking how much real wood a board holds, measure it and enter the actual numbers.
6. Worked Examples
Three hardwood boards
You need three 5/4 boards, each 7 1/2 inches wide and 9 feet 6 inches long, priced at $9.50 per board foot.
| Step | Calculation | Result |
|---|---|---|
| Thickness | 5/4 | 1.25 in |
| Length in feet | 9 + 6/12 | 9.5 ft |
| Board feet each | 1.25 x 7.5 x 9.5 / 12 | 7.42 BF |
| Total for three | 7.42 x 3 | 22.27 BF |
| Cost | 22.27 x $9.50 | $211.52 |
A table cut list with waste and cost
| Part | Qty | Thickness x width x length | Board feet |
|---|---|---|---|
| Top | 1 | 2 in x 30 in x 6 ft | 30.00 |
| Legs | 4 | 3 in x 3 in x 2.5 ft | 7.50 |
| Long aprons | 2 | 1.25 in x 4 in x 5 ft | 4.17 |
| Short aprons | 2 | 1.25 in x 4 in x 2.5 ft | 2.08 |
| Total | 43.75 | ||
Adding 25 percent for defects and cutting losses gives 43.75 x 1.25 = 54.69 board feet to buy. At $8.00 per board foot, that is 54.69 x $8.00 = $437.50. In the calculator, add the four sizes as four boards, set waste to 25, and enter the price.
A 2 x 4 x 8
Using the nominal size, 2 x 4 x 8 / 12 = 5.33 board feet. Using the actual 1.5 by 3.5 inch size, 1.5 x 3.5 x 8 / 12 = 3.5 board feet. Both are correct for different purposes, which is why it matters which one your seller uses.
7. Board Foot Charts
This chart shows the board feet in one foot of length. Multiply by the length in feet to get the board feet of a board.
| Width | 4/4 (1 in) | 5/4 (1.25 in) | 6/4 (1.5 in) | 8/4 (2 in) |
|---|---|---|---|---|
| 4 in | 0.333 | 0.417 | 0.500 | 0.667 |
| 6 in | 0.500 | 0.625 | 0.750 | 1.000 |
| 8 in | 0.667 | 0.833 | 1.000 | 1.333 |
| 10 in | 0.833 | 1.042 | 1.250 | 1.667 |
| 12 in | 1.000 | 1.250 | 1.500 | 2.000 |
For example, a 6/4 board that is 8 in wide and 10 ft long holds 1.000 x 10 = 10 board feet. This second chart gives board feet per piece for common nominal softwood sizes.
| Nominal size | 8 ft | 10 ft | 12 ft | 16 ft |
|---|---|---|---|---|
| 2 x 4 | 5.33 | 6.67 | 8.00 | 10.67 |
| 2 x 6 | 8.00 | 10.00 | 12.00 | 16.00 |
| 2 x 8 | 10.67 | 13.33 | 16.00 | 21.33 |
| 2 x 10 | 13.33 | 16.67 | 20.00 | 26.67 |
| 2 x 12 | 16.00 | 20.00 | 24.00 | 32.00 |
| 4 x 4 | 10.67 | 13.33 | 16.00 | 21.33 |
8. Board Feet to Square Feet
A board foot is volume and a square foot is area, so you cannot convert them without a thickness. Once you know the thickness, the relationship is simple, because one board foot of 1 inch stock covers one square foot.
Square feet = board feet / thickness (in)
Board feet = square feet x thickness (in)
For example, 60 board feet of 3/4 inch stock covers 60 / 0.75 = 80 square feet, and 100 square feet of 3/4 inch stock is 100 x 0.75 = 75 board feet. The Convert tab does this for any thickness, in square feet or square meters. If you only need the area of a room or a surface, our Square Footage Calculator gives it for any mix of shapes.
| Thickness | Area covered by 1 board foot |
|---|---|
| 1/4 in | 4 sq ft |
| 1/2 in | 2 sq ft |
| 3/4 in | 1.33 sq ft |
| 1 in (4/4) | 1 sq ft |
| 2 in (8/4) | 0.5 sq ft |
9. Board Feet to Cubic Feet and Other Units
Because a board foot is a volume, it converts directly to other volume units. One board foot is 144 cubic inches, which is one twelfth of a cubic foot, about 2.36 liters, or 0.00236 cubic meters. Going the other way, one cubic foot is 12 board feet and one cubic meter is about 423.8 board feet. One MBF is 1,000 board feet, or about 83.3 cubic feet.
These conversions use the full volume of the wood as if it were solid. They do not tell you how much lumber a log will yield, which depends on the log rule, sawing losses, and the mill.
10. How to Calculate Board Feet in a Log
Logs are scaled with a log rule, which is a formula or table that estimates the board feet of lumber a log can produce. Three rules are in wide use in the United States, according to Purdue Extension's guide to log and tree scaling. For all of them, D is the diameter at the small end inside the bark in inches, and L is the length in feet.
| Rule | Formula | Notes |
|---|---|---|
| Doyle | (D − 4)² × L / 16 | Simple and common in the east and south. Ignores taper and seriously under-scales small logs. |
| Scribner | (0.79D² − 2D − 4) × L / 16 | A formula that approximates the diagram-based Scribner rule. Fairly consistent for logs 16 ft or shorter and under 28 in. |
| International 1/4 in | 0.04976191LD² + 0.006220239L²D − 0.1854762LD + 0.0002591767L³ − 0.01159226L² + 0.04222222L | Allows for taper. Probably the most accurate of the three at estimating actual lumber. |
Take a log 16 inches across the small end and 16 feet long. Doyle gives (16 − 4)² × 16 / 16 = 144 board feet. The Scribner formula gives about 166, and the International rule gives about 181. For a smaller log, 10 inches across and 12 feet long, Doyle gives 27 while International gives about 46, so Doyle is far lower on small logs. The Log tab shows all three and how far each one is from the International result.
Measure the diameter at the small end, inside the bark, and average two measurements taken at right angles if the log is not round. Measure the length with a tape, and remember that a log just short of a full foot is normally scaled at the next lower foot. Always agree on a log rule before buying or selling logs. The calculator accepts logs from 6 to 60 inches across and 4 to 20 feet long. Longer logs are normally scaled as two or more shorter ones.
11. Board Foot vs Linear Foot vs Square Foot
- Linear foot: length only. A 10 ft board is 10 linear feet, whatever its width or thickness.
- Square foot: area, which is length times width. It ignores thickness.
- Board foot: volume, which is length times width times thickness, standardized to a 1 ft by 1 ft by 1 in unit.
Two boards with the same length can have very different board feet, and a board's price per board foot lets you compare them fairly.
12. Waste, Tally, and Cost
The exact board feet of your cut list is not what you should buy. Boards have defects, grain and color need matching, and every cut loses wood. Many woodworkers add roughly 15 to 30 percent to a hardwood cut list, and less for straight framing lumber. These are planning figures, so ask your supplier. The waste field in the calculator adds the percentage and shows the board feet to buy.
Dealers also tally boards in their own way. Many tally lengths to the whole foot and drop any fraction, so a board 10 ft 7 in may count as 10 ft, and they round thickness to quarters. Ask how your dealer tallies, and compare your own calculation with the tag when you pick up the lumber.
To estimate cost, multiply the board feet to buy by the price per board foot. Prices change by species, grade, thickness, and whether the board is rough or surfaced, so use your supplier's current price.
13. Common Mistakes
- Dividing by 12 when the length is in inches. Use 144 for inches and 12 for feet.
- Using surfaced thickness for hardwood. Use the quarter size, such as 4/4, not the measured 13/16 inch.
- Mixing nominal and actual sizes in the same list.
- Forgetting the quantity and counting a stack of boards as one.
- Treating a board foot like a square foot or a linear foot.
- Rounding too early, which can add up over a long list.
- Mixing log rules, or comparing one rule's scale with another's price.
- Buying the exact number. Add an allowance for defects and cuts.
14. Related Calculations and Use Cases
Board feet are used for furniture, cabinetry, flooring stock, slabs, and timber sales, and the same lumber math shows up in framing. If you are planning wall framing and need to know how many pieces to buy, our Stud Calculator counts studs and plates, and you can then price them by the piece or by the board foot.
For spray foam insulation, the term board foot also means a volume of 1 square foot at 1 inch thick, so the same area-times-thickness idea applies, but check the product's coverage information.
15. Frequently Asked Questions
A board foot is a unit of lumber volume equal to the wood in a board 1 foot long, 1 foot wide, and 1 inch thick. That is 144 cubic inches, or one twelfth of a cubic foot. It is abbreviated BF, BDFT, or FBM, and 1,000 board feet is written MBF. Hardwood is usually priced by the board foot because boards come in many widths and thicknesses.
Multiply thickness in inches by width in inches by length in feet, then divide by 12. If the length is in inches, divide by 144 instead. A board 1 inch thick, 8 inches wide, and 8 feet long is 1 x 8 x 8 / 12 = 5.33 board feet. For several boards, calculate each one, multiply by its quantity, and add the results.
Using the nominal size, a 2x4 that is 8 feet long is 2 x 4 x 8 / 12 = 5.33 board feet. The real piece measures about 1.5 by 3.5 inches, which works out to 3.5 board feet of actual wood. Softwood framing is normally sold by the piece or the linear foot, and board feet are used mainly to compare sizes and prices.
Divide the board feet by the thickness in inches. One board foot of 1 inch stock covers 1 square foot, so 60 board feet of 3/4 inch stock covers 60 / 0.75 = 80 square feet. To go the other way, multiply square feet by the thickness in inches, so 100 square feet of 3/4 inch stock is 75 board feet.
Use a log rule. Measure the diameter at the small end inside the bark, and the length in feet. The Doyle rule is (diameter - 4) squared times length divided by 16. The Scribner and International 1/4 inch rules give different answers for the same log, so always check which rule a buyer or seller is using. The calculator's Log tab shows all three.
For hardwood, board feet are figured from the rough thickness in quarters, such as 4/4 for 1 inch, even when the board is surfaced and measures less. A surfaced 4/4 board is about 13/16 inch thick but is still counted as 1 inch. For softwood framing lumber, board feet are normally figured from the nominal size, such as 2 by 4, and the actual length.
It depends on the wood and the project. Many woodworkers add roughly 15 to 30 percent to a hardwood cut list to cover defects, grain matching, and cutting losses, and less for straight framing lumber. Treat these as planning figures and ask your supplier. The calculator lets you enter your own waste percentage.
Conclusion
This board foot calculator turns thickness, width, and length into board feet, so you can price lumber fairly and plan a purchase. Enter every board in your plan, use fractions and quarters as you read them, add waste when you buy, and use the Convert and Log tabs when you need square feet, cubic units, or a log scale. Remember that board feet follow the size the seller uses, not always the size you measure, and confirm your tally with your supplier before you pay.
This calculator is for planning purposes only. Lumber sizes, tally rules, and prices vary by supplier and region. Confirm quantities with your supplier before ordering.