Board feet for softwood dimensional lumber are normally calculated on nominal size.
How board feet are calculated
BoardFootCalc multiplies thickness (inches) × width (inches) × length (feet) and divides by 12 for each row, then multiplies by the quantity and adds the rows. Cost is total board feet × your price per board foot. Cubic feet are board feet ÷ 12, and cubic metres use 1 board foot = 0.00236 m³. Nothing is rounded until the result is shown.
Common lumber sizes
| Nominal | Actual (in) | Board feet per 8 ft |
|---|---|---|
| 1×4 | ¾ × 3 ½ | 2.67 |
| 1×6 | ¾ × 5 ½ | 4 |
| 1×8 | ¾ × 7 ¼ | 5.33 |
| 1×12 | ¾ × 11 ¼ | 8 |
| 2×4 | 1 ½ × 3 ½ | 5.33 |
| 2×6 | 1 ½ × 5 ½ | 8 |
| 2×8 | 1 ½ × 7 ¼ | 10.67 |
| 2×10 | 1 ½ × 9 ¼ | 13.33 |
| 2×12 | 1 ½ × 11 ¼ | 16 |
| 4×4 | 3 ½ × 3 ½ | 10.67 |
| 6×6 | 5 ½ × 5 ½ | 24 |
Actual sizes are dry dressed sizes from the American Softwood Lumber Standard (PS 20). Board feet use nominal size, as most lumberyards tally softwood.
Log rules for a 16-foot log
| Diameter (in) | Doyle | Scribner | International ¼″ |
|---|---|---|---|
| 8 | 16 | 31 | 39 |
| 10 | 36 | 55 | 65 |
| 12 | 64 | 86 | 97 |
| 14 | 100 | 123 | 136 |
| 16 | 144 | 166 | 181 |
| 18 | 196 | 216 | 232 |
| 20 | 256 | 272 | 290 |
| 24 | 400 | 403 | 424 |
| 28 | 576 | 559 | 584 |
| 32 | 784 | 741 | 770 |
Doyle: (D − 4)² × L ÷ 16. Scribner: the common formula approximation (0.79D² − 2D − 4) × L ÷ 16, so it can differ by a few board feet from the official Scribner tables. International ¼″: Grosenbaugh's formula. All are estimates of sawn yield, not a measurement of the log's volume.
Tips for buying lumber
Measure the finished parts you need, then add allowance for planing, defects and saw kerf. Rough hardwood is usually tallied by the dealer at the rough size, and widths are often rounded to the nearest inch. Prices per board foot vary widely by species, grade and region, so use your supplier's price.
Frequently asked questions
What is the actual size of a 2×4?
1½ × 3½ inches.
What is the actual size of a 4×4?
3½ × 3½ inches.
What is the actual size of a 2×10?
1½ × 9¼ inches.
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