Home Repair and Paint Guide

Surfaced lumber isn’t the same as its nominal (advertised) size. I know it can be irritating. Every time you take measurements, you have to account for this. If you do carpentry for a living then it becomes second nature. But if you are a weekend warrior, you have to stop and think about this during the planning stage.

Lumber is sized after being rough sawed and before surfacing has taken place. A two-by-six is not 2 inches thick and 6 inches wide. After it has been dried and surfaced, it is actually 1 1/2 inches by 5 1⁄2 inches. Lumber is stocked by most dealers in lengths that range from 6 to 20 feet, normally in even increments. Studs for framing come in lengths that take the header and footer plates into consideration.

You may come across a project that requires you to supply the amount of wood in board feet. A board foot is equal to one foot square by one inch thick. There is a very simple equation that will allow you to determine how many board feet of lumber you will need for a project - Length(inches) x Width(inches) x Height(inches) / 144 = Board Feet.

Rough lumber measurements in width and thickness are used when calculating board feet, so a 2 x 4 is calculated as a 2 x 4 and not the surfaced size of 1 1/2 x 3 1/2.

Let’s determine board feet for a 2″ x 6″ x 12′ piece of lumber. Start by converting length to inches. Do this by multiplying the number of feet (12) times the number of inches in a foot (12).

12′ x 12″ = 144″

Multiply this number times the width and height.

144″ x 6″ x 2″ = 1728″

Divide this number by 144, which is the number of cubic inches in a foot.

1728″ / 144″ = 12 board feet.

When you are figuring up board feet, keep in mind a waste factor. If you purchase good clear material add about 15% for waste, if you elect to use lower grade material you will have to allow for defects and more wasted material so add about 30%.