People type this into search every day: board feet calculator.
The usual answer is “thickness times width times length, divided by 12.” That is the yard-sale version. The yard sells the stamp. The tape reads a smaller board.
This page is a labeled order. It is not a grade stamp, and it is not a structural spec.
What a board foot is
The USDA Forest Products Laboratory Wood Handbook glossary defines a board foot as a board 12 in. long, 12 in. wide, and 1 in. thick, or its cubic equivalent. That is 144 cubic inches.
In lumber practice, the same page says the count for stock 1 in. or thicker uses nominal thickness and width, and the actual length. A 2x6 you buy is not 2 in. by 6 in. after it is surfaced.
University of Wisconsin Extension’s What Is A Board Foot? note writes the single-piece formula as:
thickness (in) × width (in) × length (ft) ÷ 12
Their 2x6 example is the point I keep coming back to. On the stamp, a piece 8 ft long is 2 × 6 × 8 ÷ 12 = 8 board feet. On the tape, a surfaced 2x6 is 1.5 in. by 5.5 in. That piece is 1.5 × 5.5 × 8 ÷ 12 = 6.875 board feet.
The lumber board feet calculator uses actual dimensions, then converts the metric volume:
pieces × thickness × width × length, then × 423.776 to board feet
Thickness and width are entered in centimetres. Length is in metres. One cubic metre is 35.3147 cubic feet. One board foot is 1/12 of a cubic foot, so 35.3147 × 12 = 423.776 board feet per m³. That factor is the 144-cubic-inch definition, not a second unit.
Waste and saw kerf are excluded. The tool says that.
Fig 1
Tape to a board-foot total
Actual size first, then the 423.776 factor
12 pieces at 3.8 cm by 14 cm by 2.4 m are 0.153 m³ and 64.9 board feet.
On a US display the default 3.8 cm thickness is 1.5 in. The 14 cm width is 5.5 in. The 2.4 m length is 7.9 ft. That is a 2x6 neighbor, not a 2x6 stamp.
Example 1: the published 64.9 board-foot pack
Here are the calculator defaults:
- pieces: 12
- thickness: 3.8 cm
- width: 14 cm
- length: 2.4 m
Volume: 12 × 0.038 × 0.14 × 2.4 = 0.153216 m³
On a US display that volume is 0.2 yd³. Linear length is 12 × 2.4 = 28.8 m, shown as 94.5 ft.
Board feet: 0.153216 × 423.776 = 64.9 board ft
Calculator result
Lumber board feet
- Number of pieces
- 12 pieces
- Board thickness
- 3.8 cm
- Board width
- 14 cm
- Board length
- 2.4 m
64.9 board ft
lumber volume
- Metric volume
- 0.2 yd³
- Total linear length
- 94.5 ft
Twelve 2x6 stamps of 8 ft would have been 12 × 8 = 96 board feet. The tape is 31.1 board feet lighter than the stamp. That gap is Example 8.
Fig 2 · 1/3
How 12 boards become 64.9 board feet
Defaults: 3.8 cm by 14 cm by 2.4 m
- Board feet
| Category | Board feet |
|---|---|
| 1 piece | 5.4 |
| 6 pieces | 32.5 |
| 12 pieces | 64.9 |
One piece is 5.4 board feet.
Twelve pieces reach 64.9 board feet.
Example 2: a true 8-foot actual 2x6
Keep 12 pieces. Set the tape to a surfaced 2x6 that is really 8 ft:
- thickness: 3.81 cm (1.5 in)
- width: 13.97 cm (5.5 in)
- length: 2.4384 m (8 ft)
Board feet: 66 board ft
Linear length: 96 ft
UW Extension’s 6.875 × 12 = 82.5 would be wrong here only if you used nominal length math on mixed units. 1.5 × 5.5 × 8 ÷ 12 × 12 = 66. Same number as the calculator.
Calculator result
Lumber board feet
- Board thickness
- 3.81 cm
- Board width
- 13.97 cm
- Board length
- 2.4384 m
66 board ft
lumber volume
- Metric volume
- 0.204 yd³
- Total linear length
- 96 ft
Example 3: the stamp, typed as if it were the tape
This is the common miss. You read “2x6x8” and type 2 in. by 6 in. by 8 ft.
- thickness: 5.08 cm
- width: 15.24 cm
- length: 2.4384 m
Board feet: 96 board ft
That is the Wood Handbook practice count: nominal thickness and width, actual length. The calculator is not doing that, because its assumption line says dimensions are actual, not nominal. Type the stamp and you overstate the wood by 96 − 66 = 30 board feet on this pack.
Calculator result
Lumber board feet
- Board thickness
- 5.08 cm
- Board width
- 15.24 cm
- Board length
- 2.4384 m
96 board ft
lumber volume
- Metric volume
- 0.296 yd³
- Total linear length
- 96 ft
Fig 3 · 1/2
Stamp versus tape on twelve 8-foot 2x6s
Same 12 pieces. Only the cross-section changes.
- Board feet
| Category | Board feet |
|---|---|
| Actual 1.5×5.5 | 66 |
| Nominal 2×6 | 96 |
The tape is 66 board feet.
The 2x6 stamp is 96 board feet, 30 more.
Example 4: sixteen 2x4 studs
A framed wall often starts with 2x4s. Surfaced size is 1.5 in. by 3.5 in.
- pieces: 16
- thickness: 3.81 cm
- width: 8.89 cm
- length: 2.4384 m
Board feet: 56 board ft
Linear length: 128 ft
Nominal 2x4x8 on the same 16 pieces would be 16 × 2 × 4 × 8 ÷ 12 = 85.3 board feet. The tape is 29.3 board feet lighter.
Example 5: what if I add four more default boards
Hold 3.8 cm by 14 cm by 2.4 m. Change only the count.
- 12 pieces: 64.9 board ft
- 16 pieces: 86.6 board ft
The extra four boards add 86.6 − 64.9 = 21.7 board feet. That is 64.9 × 4 / 12, as it should be. Volume scales with the piece count when the section stays put.
Fig 4 · 1/4
Board feet as the stack grows
Same 3.8 cm by 14 cm by 2.4 m section
Board feet
- Board feet
| Point | Board feet |
|---|---|
| 4 | 21.6 |
| 8 | 43.3 |
| 12 | 64.9 |
| 16 | 86.6 |
12 pieces are 64.9 board feet.
16 pieces are 86.6 board feet.
Example 6: the same 12 boards, 3.6 m long
Keep 12 pieces and the default section. Set length to 3.6 m, which displays as 11.8 ft.
Board feet: 97.4 board ft
Linear length: 141.7 ft
3.6 / 2.4 × 64.9 = 97.35. Rounding prints 97.4. A longer stick is a larger volume. The count of pieces did not change.
Example 7: one 4x4 post
A surfaced 4x4 is 3.5 in. by 3.5 in.
- pieces: 1
- thickness: 8.89 cm
- width: 8.89 cm
- length: 2.4384 m
Board feet: 8.2 board ft
Linear length: 8 ft
Nominal 4x4x8 is 4 × 4 × 8 ÷ 12 = 10.7 board feet. One post is a small miss. A deck with a dozen posts is 12 × (10.7 − 8.2) = 30 board feet of air if you price the stamp.
Example 8: the common mistake, priced as cubic metres of “thousands”
I still see invoices that treat 1 m³ as 1,000 board feet, because both words sound like a thousand. One cubic metre is 423.776 board feet.
The default pack is 0.153216 m³. At a fake 1,000 factor that is 153.2 board feet. The calculator prints 64.9. The fake factor almost triples the volume.
The roofing material post has the same class of miss: people order from the house footprint and skip the slope. Here the miss is the unit, not the roof.
Fig 5 · 1/2
The 423.776 factor versus a fake 1,000
Default 0.153216 m³ pack
Board feet on the default pack
423.776 / m³
64.9
Fake 1,000 / m³
153.2
The real factor is 64.9 board feet.
A 1,000 factor invents 153.2 board feet.
Example 9: ten 2x10 joists at 10 ft
Surfaced 2x10 is 1.5 in. by 9.25 in.
- pieces: 10
- thickness: 3.81 cm
- width: 23.5 cm
- length: 3.048 m
Board feet: 115.6 board ft
Linear length: 100 ft
Nominal 2x10x10 on ten pieces is 10 × 2 × 10 × 10 ÷ 12 = 166.7 board feet. The tape is 51.1 board feet lighter. Joist invoices feel this gap because the nominal width is the number people remember.
Example 10: forty fence pickets
A common picket is close to 5/8 in. by 3.5 in. by 6 ft.
- pieces: 40
- thickness: 1.59 cm
- width: 8.89 cm
- length: 1.829 m
Board feet: 43.8 board ft
Linear length: 240 ft
The fence material calculator counts panels and posts, not board feet. A 32 m default fence is 18 panels and 20 posts. Buy pickets from a board-foot quote when the yard prices them that way. Buy panels when the bay width is the SKU.
The decking material calculator is the other neighbor. Its default 6 m by 4 m deck at a 14 cm face and 0.5 cm gap is 28 rows and 617.3 ft of boards after 12% waste. Convert that linear length back to board feet only if the yard still quotes the old unit.
The ten packs next to each other
| Example | Pieces | Section | Length | Board feet |
|---|---|---|---|---|
| 1. Defaults | 12 | 3.8 × 14 cm | 2.4 m | 64.9 |
| 2. Actual 2x6x8 | 12 | 1.5 × 5.5 in | 8 ft | 66 |
| 3. Nominal 2x6x8 | 12 | 2 × 6 in | 8 ft | 96 |
| 4. Actual 2x4x8 | 16 | 1.5 × 3.5 in | 8 ft | 56 |
| 5. Four extra defaults | 16 | 3.8 × 14 cm | 2.4 m | 86.6 |
| 6. Longer defaults | 12 | 3.8 × 14 cm | 3.6 m | 97.4 |
| 7. One 4x4x8 | 1 | 3.5 × 3.5 in | 8 ft | 8.2 |
| 8. Fake 1,000 / m³ | 12 | 3.8 × 14 cm | 2.4 m | 153.2 |
| 9. Actual 2x10x10 | 10 | 1.5 × 9.25 in | 10 ft | 115.6 |
| 10. Pickets | 40 | 5/8 × 3.5 in | 6 ft | 43.8 |
Open the lumber board feet calculator with the tape size, not the stamp, unless the yard is quoting nominal volume on purpose. After the wood is counted, the decking and fence tools turn a rectangle or a run into a buy list. A roof over that deck is a different order: use the roofing material post for squares and bundles.