How to Calculate Board Feet
A board foot is a unit of wood volume, not a measure of length. It represents a piece of lumber that is 1 inch thick, 12 inches wide and 1 foot long. Once you understand that, the calculation is straightforward.
For example, an 8-foot board that is 6 inches wide and 1 inch thick contains 4 board feet. If you buy six of those boards, you have 24 board feet before adding any allowance for waste.
Worked example
Suppose a project calls for 6 boards, each 8 feet long, 6 inches wide and 1 inch thick. One board is 8 × 6 × 1 ÷ 12 = 4 board feet. Six boards equal 24 board feet. If you allow 10% for defects and cutting waste, the planning quantity becomes 26.4 board feet.
The easiest way to avoid mistakes is to keep the units consistent. Length is entered in feet in the standard board-foot formula, while width and thickness are entered in inches.
When to add waste
Waste depends on the lumber, your cut plan and how much selection you need. A small furniture project using clear, straight stock may need a different allowance from a project using rough boards with knots, checks or live edges. A calculator can apply the percentage, but the percentage itself is a planning choice.
Use the MakeGauge calculator
The Board Feet Calculator lets you enter quantity, length, width, thickness, waste and price per board foot. It returns the board-foot amount and an estimated lumber cost so you can compare a project plan with a supplier quote.