Board Foot Calculator
This board foot calculator totals the board feet in a list of lumber. Enter the thickness, width, length and number of pieces for each row. It shows board feet by nominal size, which is how many lumberyards price softwood, and by actual size, which is the real volume of wood. Add a price per board foot to estimate the cost.
Quick answer: board feet = thickness (in) × width (in) × length (ft) ÷ 12. Twenty 2×4×8 studs are 106.67 board feet by nominal size and 70 by actual size.
Board feet measure volume. One board foot is a board 1 in thick, 12 in wide and 12 in long, which is 144 cubic inches. For each piece, multiply the thickness in inches by the width in inches by the length in feet, divide by 12, then multiply by the number of pieces.
Example: twenty 2×4×8 ft studs are 2 × 4 × 8 ÷ 12 = 5.3333 board feet each, so 106.67 board feet by nominal size. By actual size, 1.5 × 3.5 × 8 ÷ 12 = 3.5 board feet each, so 70 board feet.
Method
How this calculator works
A board foot is a volume, so the formula is exact. The convention is which size you put into it. The calculator shows both so you can match the way your supplier counts.
Board feet from one piece
One board foot is the volume of a board 1 in thick, 12 in wide and 12 in long: 144 cubic inches, or 1/12 of a cubic foot. With thickness and width in inches and length in feet, you divide by 12. Each row of your list is worked out, multiplied by its pieces and added to the total.
BF per piece = Thickness (in) × Width (in) × Length (ft) ÷ 12Total BF = BF per piece × Pieces, summed over all rowsNominal or actual size
Softwood dimension lumber is named by its nominal size, a 2 × 4, but a dry, surfaced one measures 1-1/2 × 3-1/2 in. Many lumberyards price softwood on the nominal size, so that is the default. Actual size gives the true volume of wood. Sources disagree on which one is the rule, so ask your supplier which basis they bill on.
Nominal BF = Nominal T × Nominal W × Length ÷ 12Actual BF = Actual T × Actual W × Length ÷ 12Actual sizes in the list
The 22 sizes in the list run from 1 × 2 to 8 × 8. Their actual sizes are for dry, surfaced softwood from the American Softwood Lumber Standard (PS 20), as compiled by ArchToolbox. That is a secondary source, because the PS 20 table itself could not be retrieved, and it matches SPIB's text: the 2 × 4 and 2 × 6 are 1/2 in narrower than their names, and the 2 × 8 to 2 × 12 are 3/4 in narrower. Green lumber is surfaced larger because it shrinks as it dries. 5/4 decking is not in the list, so use Custom size for it.
Cost, linear feet and actual volume
Cost multiplies the total on the basis you picked by the price you enter, and leaves out tax, delivery and waste. Linear feet are the lengths times the pieces. Actual volume is the actual-size board feet divided by 12, in cubic feet. Boards can be up to 3 in longer than their nominal length, so enter the length as ordered.
Cost = Total BF × Price per BFActual volume (ft³) = Actual BF ÷ 12Nominal and actual side by side, for an 8 ft piece
| Nominal size | Actual size (in) | Board feet, nominal | Board feet, actual |
|---|---|---|---|
| 1×6 | 3/4 × 5-1/2 | 4 | 2.75 |
| 1×12 | 3/4 × 11-1/4 | 8 | 5.63 |
| 2×4 | 1-1/2 × 3-1/2 | 5.33 | 3.5 |
| 2×6 | 1-1/2 × 5-1/2 | 8 | 5.5 |
| 2×8 | 1-1/2 × 7-1/4 | 10.67 | 7.25 |
| 2×10 | 1-1/2 × 9-1/4 | 13.33 | 9.25 |
| 2×12 | 1-1/2 × 11-1/4 | 16 | 11.25 |
| 4×4 | 3-1/2 × 3-1/2 | 10.67 | 8.17 |
What each field does
| Field | What to enter |
|---|---|
| Size basis for board feet | Nominal size is the default and how many lumberyards price softwood. Actual size is the true volume of the wood. The total and the cost use the basis you pick, and the other basis appears underneath as a second result. A Custom size row is the same in both. |
| Size (each row) | Standard lumber gives you 22 nominal sizes, from 1 × 2 to 8 × 8. Custom size lets you type a thickness and width for hardwood, 5/4 decking or anything not in the list. |
| Nominal size | Pick the size by its name, such as 2 × 4. The list shows the actual size next to each name. |
| Thickness and Width | Custom size only. Inches in the US view or millimeters in the metric view. They are used exactly as typed, in both bases. Hardwood is usually priced on rough thickness, where 4/4 is 1 in and 5/4 is 1.25 in. |
| Length | Enter the length as ordered, in feet and inches in the US view or meters and centimeters in the metric view. An 8 ft (2.4 m) piece is a common stud length. |
| Pieces | How many identical pieces are in that row. |
| Add row and Remove | Use one row for each size and length in your list. You can add up to 30 rows, and the total adds them all. |
| Price per board foot | Optional, in the Price section. Adds an estimated cost from the board feet on your chosen basis. Ask your supplier for the price. Tax, delivery and waste are not included. |
Worked example: twenty 2×4×8 studs
Arithmetic checkedNominal basis is the default. The totals match the calculator's own example: 106.67 board feet nominal and 70 actual. The price is a round number to show the arithmetic, not a market price.
| Step | Math | Result |
|---|---|---|
| Pieces | entered | 20 × 2×4×8 ft |
| Nominal board feet, one piece | 2 × 4 × 8 ÷ 12 | 5.3333 BF |
| Nominal total | 5.3333 × 20 | 106.67 BF |
| Actual board feet, one piece | 1.5 × 3.5 × 8 ÷ 12 | 3.5 BF |
| Actual total | 3.5 × 20 | 70 BF |
| Difference between the two bases | 106.67 − 70 | 36.67 BF |
| Linear feet | 8 × 20 | 160 ft |
| Actual volume | 70 ÷ 12 | 5.83 ft³ |
| Cost at a round $10 per board foot (not a market price) | 106.67 × 10 | $1,066.67 |
| You would see | 106.67 BF nominal, 70 BF actual | |
Disclaimer
Results are planning estimates based on the dimensions and assumptions you enter. They are not engineering, structural or building-code advice. Product yields, densities and coverage vary by manufacturer, batch and site conditions. Check product labels, your supplier and your local building department before you order materials or start work. Read the full calculation disclaimer.
Accuracy
What affects your estimate
The formula is exact. What moves the answer is the size basis, the mix of pieces and how your supplier sells the wood.
The size basis changes the total
The same twenty studs are 106.67 board feet nominal and 70 actual, a gap of 36.67. If you are checking a price per board foot, use the basis the seller uses. If you want the real amount of wood, use actual. Also confirm that the quote is by board foot and not per piece or per linear foot.
A mixed list adds up row by row
Take 20 pieces of 2×4×8, 10 pieces of 2×6×12 and 10 custom boards of 1 × 7 in × 8 ft. The nominal rows are 106.67, 120 and 46.67 board feet, which total 273.33 on the unrounded values. The actual rows are 70, 82.5 and 46.67, which total 199.17. The custom boards count the same on both bases.
Hardwood is priced on rough thickness
Hardwood is sold in quarters of an inch: 4/4 is 1 in and 8/4 is 2 in. Use Custom size with the rough thickness. A 4/4 board 7 in wide and 8 ft long is 1 × 7 × 8 ÷ 12 = 4.667 board feet. Ask whether the price is for rough or surfaced stock.
Length and condition matter
Enter the length you will order. Green, rough-sawn and reclaimed lumber can differ from the dry, surfaced sizes in the list, so measure those boards and use Custom size.
Board feet describe how much wood there is. They say nothing about species, grade or spans, which are structural questions for the grade stamp, your building department or a licensed engineer. Estimating board feet in a standing tree or a log uses log rules and is not covered here.
Common mistakes
Checking a nominal price with actual sizes
If the yard prices on nominal size and you measure the boards, you get 70 board feet instead of 106.67 for the same studs, and the price looks wrong. Match the basis to the quote.
Treating board feet as linear feet
An 8 ft 2×4 is 8 linear feet but 5.33 board feet. A board foot is a volume, so thickness and width count. The guide on how to calculate linear feet covers running length.
Entering the length in the wrong unit
The formula divides by 12 only when the length is in feet. The calculator converts for you, but check that the length field is in feet and inches (or meters and centimeters), not a number of inches typed as feet.
Using it for logs or standing trees
This calculator works on boards you can measure. A log or a tree needs a log rule that predicts the board feet it will saw into, which is a different method.
Forgetting your own waste allowance
The calculator adds no waste. If you will cut around defects or make many cuts, add an allowance of your own to the pieces.
Questions people ask
How do I calculate a board foot?
Multiply the thickness in inches by the width in inches by the length in feet, then divide by 12. A board 1 in × 12 in × 12 in is exactly 1 board foot, which is 144 cubic inches. The guide on how to calculate board feet adds a size table and hardwood examples.
How many board feet is a 2×4×8?
It is 5.33 board feet by nominal size (2 × 4 × 8 ÷ 12) and 3.5 by actual size (1.5 × 3.5 × 8 ÷ 12). Twenty of them are 106.67 nominal and 70 actual. Counting studs for a wall instead? How many studs you need gives the count at 16 and 24 in on center.
How many board feet is a 2×4×10?
It is 6.67 board feet nominal (2 × 4 × 10 ÷ 12) and 4.375 actual (1.5 × 3.5 × 10 ÷ 12).
How many square feet is 1 board foot?
It depends on the thickness. The face area in square feet is the board feet divided by the thickness in inches. A board 1 in thick has 1 ft² of face per board foot, a 2 in board has 0.5 ft², and a 1/2 in board has 2 ft².
Should I use nominal or actual size for board feet?
Use the basis your supplier bills on. Many lumberyards price softwood on nominal size, so nominal is the calculator's default, but sources disagree. Use actual size when you need the real volume of wood. Hardwood is priced on rough thickness, so use Custom size for it.
Related calculators and guides
Sources
Where the numbers come from
- SPIB, Nominal vs. Actual Lumber Sizes how PS 20 lists nominal and dressed sizes, including the 2×4 and 2×6 being 1/2 in narrower, accessed October 16, 2026.
- ArchToolbox, Lumber Dimensions dry, surfaced actual sizes citing PS 20 (a secondary source) and the allowance for lengths up to 3 in over nominal, accessed October 16, 2026.
- Penn State Extension, Valuing Standing Timber the board foot as 1 in × 12 in × 12 in, accessed October 16, 2026.
- Ohio State University Extension, Measuring Standing Trees the board foot definition and the formula with length in feet, accessed October 16, 2026.
- NIST Handbook 44 (2026), Appendix C 1,728 cubic inches per cubic foot, behind the volume conversion, accessed October 16, 2026.