Board Foot Calculator
80 board feet.
| Step | Value |
|---|---|
| Nominal size | 2″ × 6″ × 8 ft |
| Actual dressed size what it really measures | 1.5″ × 5.5″ — board feet still use the nominal size |
| Board feet per piece | (2 × 6 × 8) ÷ 12 = 8 bf |
| Total for 10 pieces | 80 board feet |
A board foot is 144 cubic inches of lumber — nominally 1 in thick × 12 in wide × 1 ft long. Board feet use nominal dimensions, so a 2×4 is billed as 2 in × 4 in even though it actually measures 1½ × 3½ after drying and planing. That is not a rounding error in your favour or against it; it is simply the unit the trade prices in, and both the mill and the yard use it the same way. Hardwood is the exception worth knowing: it is sold in quarters of an inch of rough thickness, so 4/4 is one inch, 8/4 is two, and the board really is that thick before surfacing.
Enter your lumber dimensions and quantity to get total board feet and cost — with a nominal versus actual size reference for dimensional lumber.
How to use this calculator
- Enter thickness and width in inches, using the nominal size — 2 and 6 for a 2×6, not 1.5 and 5.5.
- Enter the length and switch the units between feet and inches to match how your board is listed.
- Set the quantity of identical pieces.
- Add a price per board foot to price the order. For a mixed load, run each size separately and add the totals.
The formula
Board feet = (Thickness in × Width in × Length ft) ÷ 12 · or (T × W × L in) ÷ 144
Both give the same answer — a board foot is 144 cubic inches.
Worked example — ten 2 × 6 × 8 ft boards
- Per piece: (2 × 6 × 8) ÷ 12 = 8 board feet
- Ten pieces: 8 × 10 = 80 board feet
- At $4.50/bf: $360
Each of those boards actually measures 1½ × 5½ inches, so the real volume is 5.5 board feet, not 8. That is not an error to correct — the price per board foot already accounts for it, and every yard quotes the same way. What matters is that you compare like with like.
Nominal versus actual: the 2×4 that isn't
Softwood dimensional lumber is named for its rough green size, then dried and planed on all four sides. What arrives is noticeably smaller than the name:
| Nominal | Actual | Nominal | Actual |
|---|---|---|---|
| 1 in | 3/4 in | 2 × 4 | 1½ × 3½ |
| 2 in | 1½ in | 2 × 6 | 1½ × 5½ |
| 4 in | 3½ in | 2 × 8 | 1½ × 7¼ |
| 6 in | 5½ in | 2 × 10 | 1½ × 9¼ |
| 8 in | 7¼ in | 2 × 12 | 1½ × 11¼ |
| 10 in | 9¼ in | 4 × 4 | 3½ × 3½ |
Notice the pattern breaks above 6 inches: boards up to 6 in lose half an inch, wider ones lose three quarters. This catches people laying out framing — four 2×6s stacked are 6 inches, but four 2×8s are 6½, not 7.
Hardwood is measured differently
Hardwood is sold in quarters of an inch of rough thickness, and unlike softwood nominal sizes these are real measurements before surfacing:
| Quarter | Rough thickness | Typical surfaced (S2S) |
|---|---|---|
| 4/4 | 1 in | 13/16 in |
| 5/4 | 1¼ in | 1 1/16 in |
| 6/4 | 1½ in | 1 5/16 in |
| 8/4 | 2 in | 1¾ in |
| 12/4 | 3 in | 2¾ in |
Hardwood also comes in random widths and lengths rather than standard sizes, which is precisely why it is sold by the board foot. You are buying a volume of wood, not a count of pieces, and the dealer tallies each board individually.
Board feet, linear feet, and square feet
Three units that get mixed up constantly, and the mix-up is always expensive:
- Board foot — volume. 144 cubic inches. Used for lumber priced by the mill or hardwood dealer.
- Linear foot — length only, ignoring thickness and width. Used for trim, moulding, and decking. A 1×12 and a 1×4 are identical by the linear foot and differ threefold by the board foot.
- Square foot — area. Used for sheet goods, flooring, and siding coverage.
Before comparing two quotes, check which basis each uses. A price that looks half as much per linear foot may be for a board half the width.
How much extra to buy
Waste allowance depends entirely on what you are doing with the wood:
- Dimensional softwood, cut to length: 10% covers ordinary offcuts.
- Hardwood milled to size: 20 to 30%. Rough boards arrive with wane, checks, and irregular edges, and squaring them up eats material.
- Working around defects for clear stock: 40% is normal, more for figured or character grades.
- Anything with a repeating pattern or grain match: add more again, because the offcuts are rarely usable elsewhere.
Common mistakes to avoid
- Using actual dimensions instead of nominal. Entering 1.5 × 5.5 for a 2×6 understates board feet by 31% and will not match any quote you are given.
- Dividing by 12 when the length is in inches. Use 144, or switch the length units here.
- Comparing a board-foot price to a linear-foot price. They are not the same unit and the cheaper-looking one often is not.
- Forgetting waste on hardwood. A 100 board foot project needs 125 to 130 board feet of rough stock.
How we calculate this
Board feet = (thickness in inches × width in inches × length in feet) ÷ 12, multiplied by the quantity. When the length is given in inches the divisor becomes 144, since a board foot is 144 cubic inches by definition. Dimensions are nominal, which is how lumber is priced everywhere it is sold — a 2×4 is billed as 2 in × 4 in despite measuring 1½ × 3½. Where the entered thickness and width match a standard dimensional size, the calculator also shows what that piece actually measures, so the difference is visible rather than surprising.
Sources
Frequently asked questions
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in feet, then divide by 12. A 2 by 6 that is 8 feet long is (2 × 6 × 8) ÷ 12 = 8 board feet. If your length is in inches instead, divide by 144 rather than 12 — a board foot is 144 cubic inches either way.
What is a board foot?
A board foot is a unit of lumber volume equal to 144 cubic inches — nominally a piece 1 inch thick, 12 inches wide, and 1 foot long. It is how lumber is priced at the mill and at hardwood dealers, because it lets boards of wildly different dimensions be compared and sold on the same basis.
Do board feet use nominal or actual dimensions?
Nominal. A 2 by 4 is billed as 2 inches by 4 inches even though it actually measures 1½ by 3½ after drying and planing. This is not a trick — the mill and the yard both use nominal sizes consistently, so prices already reflect it. Hardwood is different: it is sold in quarters of an inch of rough thickness, so 4/4 really is one inch thick before surfacing.
How many board feet are in a 2x4?
An 8-foot 2 by 4 is 5.33 board feet: (2 × 4 × 8) ÷ 12. A 10-footer is 6.67 and a 12-footer is 8. Multiply by your quantity for the total — a bunk of 100 eight-foot 2 by 4s is 533 board feet.
What does 4/4 mean in lumber?
Four quarters, meaning one inch of rough thickness. Hardwood is sold this way: 4/4 is 1 inch, 5/4 is 1¼, 6/4 is 1½, 8/4 is 2 inches, and so on. Unlike softwood nominal sizes, these are the actual rough thickness before surfacing — a 4/4 board really does start at one inch and finishes around 13/16 after planing both faces.
How do I price lumber by the board foot?
Multiply total board feet by the price per board foot. The reason hardwood dealers quote this way rather than by the piece is that boards come in random widths and lengths — you buy volume, not units. Softwood dimensional lumber is usually priced per piece or per linear foot instead, so convert before comparing two quotes.
Is a board foot the same as a linear foot?
No, and confusing them is expensive. A linear foot is just length, regardless of thickness or width. A board foot is volume. A 1 by 12 and a 1 by 4 are both one linear foot per foot of length, but the 1 by 12 is three times the board feet — and three times the price. Always check which basis a quote uses.
How much waste should I add to a lumber order?
For dimensional softwood cut to length, 10% covers ordinary offcuts. For hardwood being milled to size, plan on 20 to 30%: rough boards come with wane, checks, and irregular edges, and you lose material squaring them up. If you are working around defects to get clear stock, 40% is not unusual.