It’s easier to first determine the roof’s area in square inches, then do all the calculations and then convert the answer to linear feet; that way you avoid working with fractions.
You're ready to re-do your roof and it's time to purchase the materials. You've measured your roof and calculated the area in square feet. When you get to the home improvement store, you find out the roofing materials are sold by the linear foot. It's easy to convert a measurement in terms of square feet to one in terms of linear feet.
Measure the length and width of your roof in inches. Multiply the roof's length by its width to get the total roof area in terms of inches.
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Determine the width in inches of your proposed roof shingles or other materials.
Divide the total roof area in inches (the figure you calculated in Step 1) by the width of your proposed shingles in inches (determined in Step 2). This figure is the area of your roof in linear inches.
Divide the area of your roof in linear inches (calculated in Step 3) by 12 to convert the inches to feet. The resulting figure is the area of your roof in linear feet. This is the figure you need to determine the correct amount of materials when purchasing by the linear foot.
Sharon Sweeny has a college degree in general studies and worked as an administrative and legal assistant for 20 years before becoming a professional writer in 2008. She specializes in writing about home improvement, self-sufficient lifestyles and gardening.