When you're buying lumber for a project or material for a floor, you may see the price quoted based on linear feet or square feet. Linear feet indicates length and square feet is a measure of area, so the difference can be confusing. You usually see the price quoted in square feet for products like flooring and plywood, while trim and dimensioned lumber are usually sold by the linear foot. Carpeting, linoleum and other sheet flooring may be sold by the linear foot, but it's with the understanding that you multiply the length of the roll by the amount of linear feet you purchase to get the number of square feet you need.
Measuring in Linear Feet
Linear feet is a one-dimensional measurement, with "linear" describing a straight line. For example, when finding the length of a bedroom wall, you would measure from one corner to another and express the length in feet. You also use linear feet when calculating how much trim you need for, say, a window or a wall.
Measuring in Square Feet
Because area is a two-dimensional measurement, you need to make two measurements to calculate it. In most home-improvement situations, that's usually the length and width of a room, a countertop or another surface. To calculate the area of a room in square feet, you need to make your measurements in feet.
For example, the area of a room that measures 12 linear feet by 8 linear feet is 96 square feet. If a room is 12' 6" by 8' 3", you can either convert the measurements to decimal notation and multiply, or you can convert both measurements to inches, multiply them, and convert the result back to feet.
Method 1: 12' 6" x 8' 3" = 12.5' x 8.25' = 103.125 square feet.
Method 2: 12' 6" x 8' 3" = 150" x 99" = 14,850 square inches = 103.125 square inches.
Purchasing by the Square Foot
Materials such as carpeting and fabrics may be sold either by the linear foot or the square foot. When sold by the square foot, divide the length of the roll into the total area to be covered to get the number of linear feet you need.
When you're buying hardwood flooring, simply look on the box to find out how many square feet the flooring in the box will cover. For most products, it's usually between 18 and 22 square feet.