Roof Measurement for Dummies

rolled roofing

If the truth be told, we've just plain lost track of the number times we've run across eHowians who simply don't get the notion of linear feet (or yards, meters, furlongs, whatever). It's a big number, though. We were looking for a quick and dirty DotD nomination today, and one of the kids pointed in the direction of yet another freelancer who's ignorant on the topic: so here's Sharon Sweeny and her Hunker.com post, "How to Calculate Roof Measurement in Linear Feet."

We'll get this information out of the way right up front: we don't know why the OQ wanted to calculate the roof size in linear feet, but we suspect it was because he wanted to lay rolled roofing. Most rolled roofing is 36 inches wide, so all the OQ needed to do was divide the width of the roof (in feet) by 3 and multiply that number, rounded up to the nearest whole number, by the length of the roof. For example, a roof is 41' by 55': the number of linear feet of rolled roofing needed is 41/3 = 13.67, rounded up to 14, multiplied by 55 = 770 linear feet of 3-foot-wide material, or 8 rolls 100 feet long. Easy-peezy...

But that's not what Sweeny said. No, Sharon wanted you to:

1. Calculate the roof's area in square inches
2. Measure your shingle width in inches
3. Divide the area of the roof by the shingle width to determine "area of your roof in linear inches. "
4. Divide linear inches by twelve.

According to Sweeney,

"This is the figure you need to determine the correct amount of materials when purchasing by the linear foot."

The problem? You don't buy shingles by the linear foot, you buy them by the square, which is 100 square feet (typically three bundles). The sample roof above? 23 squares or about 70 bundles.

We suspect that you probably want to ask a roofer (or at least a handyperson) that question, not a "professional writer"... errr, a Dumbass of the Day.

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