Lumber Calculator

How board feet work

One board foot is a volume of 144 cubic inches — conventionally imagined as a board 12 in wide, 12 in long and 1 in thick. The formula scales that to any stock:

BF = T(in) × W(in) × L(ft) × pieces ÷ 12

Note the unit mix: thickness and width in inches, length in feet, divided by 12. Two gotchas. First, nominal vs actual: a "2×6" measures 1.5 × 5.5 in actual, but hardwood is priced on nominal dimensions while construction lumber is sold by the piece — check which convention your supplier uses. Second, thickness above 1 in counts in quarters for hardwood: 8/4 stock is two inches thick.

Worked example

Twenty boards of 8/4 (2 in) × 6 in × 10 ft: each board is 2 × 6 × 10 ÷ 12 = 10 bf, so the stack totals 200 board feet. At $4.50/bf that is $900 before tax — and note that many yards add a per-board or tally surcharge for widths over 9 in. In metric terms, 200 bf ≈ 0.472 m³.

Estimating a project

Woodworkers add a waste factor of 20–30% for rough lumber (defects, planing, offcuts) versus 10–15% for S4S dimensional stock. Multiply your parts-list volume by (1 + waste) before pricing, then round up to the next 5 bf — yards tally in whole board feet and rarely break them.

Frequently asked questions

1. What is a board foot?

A volume of lumber equal to 144 cubic inches — e.g. a board 12 in × 12 in × 1 in. The formula is thickness(in) × width(in) × length(ft) ÷ 12, multiplied by the piece count.

2. Is board foot based on nominal or actual size?

Hardwood is priced on nominal thickness (8/4 = 2 in) and measured width. Construction lumber like 2×4s is sold by the piece instead, even though its actual size is smaller.

3. How many board feet is a 2×6?

A 2×6 that is 8 ft long is 2 × 6 × 8 ÷ 12 = 8 board feet by nominal dimensions. Actual-dressed 1.5 × 5.5 stock would be 5.5 bf, which is why the nominal convention matters.

4. How much waste should I add for a lumber order?

20–30% over the parts-list volume for rough hardwood (defects and milling losses) and 10–15% for straight dimensional lumber. Rounding up to the yard's tally increments avoids a second trip.