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Construction & Lumber Calculator

Calculate board feet, linear feet and cost for a lumber order. Enter the dimensions and price, then press Calculate.

Written and reviewed by SM Arijul Islam · Last reviewed 29 October 2026 · Editorial standards · Report an error

About the Construction & Lumber Calculator

Hardwood is priced by the board foot, a volume of 144 cubic inches. A 1-inch-thick board that is 12 inches wide and 12 inches long is one board foot; so is a 2 × 6 that is 12 inches long, because 2 × 6 × 12 ÷ 12 = 12. Softwood construction lumber is more often priced per linear foot or per piece.

The dimensions used for board feet are nominal. A 2 × 4 is 1.5 × 3.5 inches after planing, but it is still sold and priced as a 2 × 4. This calculator uses the dimensions you enter, so enter nominal sizes for a board-foot quote and actual sizes for a volume check.

How the calculation works

Board feet per piece = thickness (in) × width (in) × length (ft) ÷ 12.
Total board feet = board feet per piece × quantity.
Linear feet = length (ft) × quantity.
Cost = total board feet × price per board foot.

Reference values

Common lumber dimensions
Nominal size	Actual size	Board feet per 8 ft
2 × 4	1.5 × 3.5 in	5.33 bf
2 × 6	1.5 × 5.5 in	8.0 bf
2 × 8	1.5 × 7.25 in	10.67 bf
2 × 10	1.5 × 9.25 in	13.33 bf
4 × 4	3.5 × 3.5 in	10.67 bf
1 × 6	0.75 × 5.5 in	4.0 bf

Worked example: ten 2 × 10 joists

A 2 × 10 × 16 ft joist is 2 × 10 × 16 ÷ 12 = 26.67 board feet. Ten of them are 266.7 bf; at $6/bf that is $1,600. The same order is 160 linear feet. If the yard prices by the piece instead, compare the piece price with the board-foot total rather than assuming the units match.

Board feet are calculated on nominal dimensions because that is how hardwood is sold. The planed board is smaller—a 2 × 10 is actually 1.5 × 9.25 in—so a volume check on the delivered timber will be lower than the board-foot quote. That is expected, not a short shipment.

Waste, cuts and ordering

Board-foot totals describe the timber in the finished frame, not what you buy. Straight runs with few cuts waste perhaps 5%, a simple stud wall about 10%, and roofs, stairs or angled bracing 15% or more because offcuts cannot be reused. Add the allowance before pricing, and add it again for anything that must be selected for straightness or appearance.

Ordering in standard lengths also changes the count. Two 8 ft boards can replace one 16 ft board only if a joint is acceptable at that point, and a joint in a beam or a visible rail usually is not. Work out the cut list first, then round each length up to what the yard actually stocks.

Frequently asked questions

Why is a 2 × 4 not 2 × 4?

It is planed down after sawing. The nominal size is the rough green dimension used for pricing and ordering.

How many board feet in a 2 × 4 × 8?

2 × 4 × 8 ÷ 12 = 5.33 board feet using nominal dimensions. Using actual 1.5 × 3.5 gives 3.5 board feet.

Should I add waste?

Yes for cuts and defects. Add 5–10% for straightforward framing and more for complex layouts.

Do I use nominal or actual thickness for board feet?

Use nominal dimensions for a board-foot quote, because that is how hardwood is sold. Use actual dimensions if you are checking the volume of material you received.

Sources and standards

Nominal lumber sizes are the rough-sawn dimensions, before planing: a 2x4 finishes at 38 x 89 mm and a 1x6 at 19 x 140 mm. The American Wood Council publishes the dressed sizes and the span tables that govern structural use, and the page treats every size as nominal rather than exact.