A square foot is the unit of area used in the United States and some other countries, while a linear foot is the unit of length. Apparently the direct conversion between area and length is not possible until you add the second dimension to the unit of length. Consider the following example: wooden planks are often priced and sold using linear foot units. Calculate how many wooden planks are needed to make a fence that is 20 feet by 1.5 feet.

Multiply the dimensions of the fence to calculate its area in square feet. Area = 20 x 1.5 = 30 square feet.

Obtain the plank width (typically in inches) from specifications or elsewhere. Divide it by 12 to calculate it in feet. Note that the width is the second dimension that will allow the conversion. For example, the width is 1.5 inches, that is, 1.5 / 12 = 0.125 linear feet.

Divide the area (Step 1) by the width (Step 2) to convert square feet to linear feet. In our example, area (square feet) = 30 / 0.125 = 240 linear feet.