Board foot calculator with a multi-line lumber takeoff and the nominal vs actual size chart from 1x2 to 6x6 (PS 20 dry sizes). One board foot is 144 cubic inches of nominal lumber: a 2x12 × 8 ft is 16 BF, a 2x4 × 8 ft is 5-1/3 BF, and that 2x4 actually measures 1-1/2" × 3-1/2".
4 lines · 10% waste
Sort any column, print a shop sheet, download CSV. Click a row to load it in the calculator.
| 3/4" × 1-1/2" | 19 × 38 mm | 0.167 | 1.33 | 2.00 | 2.67 | ||
| 3/4" × 2-1/2" | 19 × 64 mm | 0.250 | 2.00 | 3.00 | 4.00 | ||
| 3/4" × 3-1/2" | 19 × 89 mm | 0.333 | 2.67 | 4.00 | 5.33 | ||
| 3/4" × 5-1/2" | 19 × 140 mm | 0.500 | 4.00 | 6.00 | 8.00 | ||
| 3/4" × 7-1/4" | 19 × 184 mm | 0.667 | 5.33 | 8.00 | 10.67 | ||
| 3/4" × 9-1/4" | 19 × 235 mm | 0.833 | 6.67 | 10.00 | 13.33 | ||
| 3/4" × 11-1/4" | 19 × 286 mm | 1.000 | 8.00 | 12.00 | 16.00 | ||
| 1" × 3-1/2" | 25 × 89 mm | 0.417 | 3.33 | 5.00 | 6.67 | ||
| 1" × 5-1/2" | 25 × 140 mm | 0.625 | 5.00 | 7.50 | 10.00 | ||
| 1-1/2" × 1-1/2" | 38 × 38 mm | 0.333 | 2.67 | 4.00 | 5.33 | ||
| 1-1/2" × 2-1/2" | 38 × 64 mm | 0.500 | 4.00 | 6.00 | 8.00 | ||
| 1-1/2" × 3-1/2" | 38 × 89 mm | 0.667 | 5.33 | 8.00 | 10.67 | ||
| 1-1/2" × 5-1/2" | 38 × 140 mm | 1.000 | 8.00 | 12.00 | 16.00 | ||
| 1-1/2" × 7-1/4" | 38 × 184 mm | 1.333 | 10.67 | 16.00 | 21.33 | ||
| 1-1/2" × 9-1/4" | 38 × 235 mm | 1.667 | 13.33 | 20.00 | 26.67 | ||
| 1-1/2" × 11-1/4" | 38 × 286 mm | 2.000 | 16.00 | 24.00 | 32.00 | ||
| 3-1/2" × 3-1/2" | 89 × 89 mm | 1.333 | 10.67 | 16.00 | 21.33 | ||
| 3-1/2" × 5-1/2" | 89 × 140 mm | 2.000 | 16.00 | 24.00 | 32.00 | ||
| 3-1/2" × 7-1/4" | 89 × 184 mm | 2.667 | 21.33 | 32.00 | 42.67 | ||
| 3-1/2" × 9-1/4" | 89 × 235 mm | 3.333 | 26.67 | 40.00 | 53.33 | ||
| 3-1/2" × 11-1/4" | 89 × 286 mm | 4.000 | 32.00 | 48.00 | 64.00 | ||
| 5-1/2" × 5-1/2" | 140 × 140 mm | 3.000 | 24.00 | 36.00 | 48.00 |
Board feet use the nominal size: a 2x4 counts as 2 × 4 even though it measures 1-1/2" × 3-1/2". 5/4 decking counts as 1.25" thick and measures 1".
05 / Field guide
A board foot is a volume, 144 cubic inches: a piece one foot long, one foot wide and one inch thick. Softwood dimension lumber is counted on its nominal size, the size before drying and planing, so a 2x4 counts as 2" × 4" even though it measures 1-1/2" × 3-1/2". The takeoff calculator adds up board feet line by line and the chart lists the real sizes you will be cutting.
Multiply nominal thickness by nominal width (inches) by length, then divide by 144 if the length is in inches or by 12 if it is in feet. A 2x12 × 8 ft is 2 × 12 × 8 ÷ 12 = 16 board feet; a 2x4 × 8 ft is 5-1/3.
BF = T × W × L(in) ÷ 144 = T × W × L(ft) ÷ 12 (nominal inches)
Sawmills cut green boards close to the nominal size, then the wood shrinks as it dries and loses more when it is planed smooth. The American Softwood Lumber Standard (PS 20) fixes the dry dressed sizes: 1x boards are 3/4" thick, 2x lumber 1-1/2", 4x 3-1/2". Widths up to 6" lose 1/2" (a 2x6 is 5-1/2"), and 8" and wider lose 3/4" (a 2x8 is 7-1/4", a 2x12 11-1/4").
5/4 decking is the odd one: it is counted as 1-1/4" but measures 1" thick, which is why the stair calculator takes 1" off the bottom riser for 5/4 treads.
Hardwood is sold rough by the board foot in quarters of an inch: 4/4 is 1" rough, 8/4 is 2". Board feet use the rough thickness, and widths are random, so measure each board and add them up.
Allow 10% for framing and 15% for decking with angled ends or picture-frame borders. Order lengths that cut cleanly: three 36" treads come out of a 10 ft board with room for the kerfs and end checks, four out of a 12.
Many yards price dimension lumber per piece or per linear foot rather than per board foot. The takeoff converts any line to board feet so you can compare quotes on the same basis.
Four 2x12 × 8 ft stringers are 4 × 16 = 64 board feet. Four 5/4 × 6 × 12 ft boards for the treads are 7.5 board feet each, 30 in all, and two 4x4 × 8 ft posts add 21-1/3. With 10% waste the stair is about 127 board feet, which is the number to compare when one yard quotes per piece and another per board foot.
Questions
Multiply the nominal thickness and width in inches by the length in feet and divide by 12. For several pieces, multiply by the count. A 2x6 × 10 ft is 2 × 6 × 10 ÷ 12 = 10 board feet.
5-1/3 board feet (2 × 4 × 8 ÷ 12 = 5.33).
32 board feet (2 × 12 × 16 ÷ 12).
Nominal sizes describe the rough green board. After drying and planing, a 2x4 measures 1-1/2" × 3-1/2" under the PS 20 softwood standard.
1-1/2" thick by 5-1/2", 7-1/4", 9-1/4" and 11-1/4" wide.
Multiply the linear feet by the board feet per foot of that size, which is nominal thickness × width ÷ 12. A 2x8 is 1.333 BF per foot, so 60 linear feet of 2x8 is 80 board feet.
Raised decks, basements and storeys