Everyday
Lumber Calculator
Turn a cut list of nominal lumber sizes into board feet, waste, and cost, with a nominal versus actual size reference.
| Nominal | Actual (in) | Actual (mm) |
|---|---|---|
| 1x4 | 3/4 x 3-1/2 | 19 x 89 |
| 1x6 | 3/4 x 5-1/2 | 19 x 140 |
| 2x4 | 1-1/2 x 3-1/2 | 38 x 89 |
| 2x6 | 1-1/2 x 5-1/2 | 38 x 140 |
| 2x8 | 1-1/2 x 7-1/4 | 38 x 184 |
| 2x10 | 1-1/2 x 9-1/4 | 38 x 235 |
| 2x12 | 1-1/2 x 11-1/4 | 38 x 286 |
| 4x4 | 3-1/2 x 3-1/2 | 89 x 89 |
| 6x6 | 5-1/2 x 5-1/2 | 140 x 140 |
How it works
Behind the numbers
One board foot is a slab 12 by 12 by 1 inches, and the formula is thickness times width times length in feet, divided by 12, using the nominal size. A 2x4 at 8 feet is 2 times 4 times 8 divided by 12, or 5.33 board feet. The cut list applies this to every line and multiplies by quantity.
Nominal size is the name, not the measurement: surfaced lumber is milled smaller, so a 2x4 actually measures 1-1/2 by 3-1/2 inches (38 by 89 mm). Yards still bill board feet on the nominal size, which is why the cut list asks for nominal dimensions. The reference table lists the common sizes in inches and millimeters.
The waste allowance covers offcuts and bad boards; 10% suits straight framing, 15% or more suits angled cuts and decks. The buy total is the subtotal plus waste, and cost is the buy total times your price per board foot. Lengths can be entered in feet or meters.
FAQ
Questions, answered
How do you calculate board feet?
Multiply thickness by width (both in inches, nominal size) by length in feet, then divide by 12. A 2x6 at 10 feet is 2 x 6 x 10 / 12 = 10 board feet.
Why is a 2x4 not actually 2 by 4 inches?
Rough-sawn lumber starts at the full nominal size, then surfacing on all four sides removes about half an inch. A finished 2x4 measures 1-1/2 by 3-1/2 inches. The name stuck because yards bill and price by it.
Are board feet calculated on nominal or actual size?
Nominal. Board footage is a billing unit, so the 2x4 in the formula is 2 by 4, even though the board in your hand is smaller. This matches NHLA lumber rules.
How much waste should I add when buying lumber?
10% is standard for straight framing cuts. Raise it to 15% or more for decks, fences, or anything with many angled cuts, and buy a few extra boards if the project cannot pause for a second trip.