Things You'll Need
Note that in the above calculation we came up with a partial sheet but rounded up for the amount of pieces. This is common practice as the width can be changed by overlapping the sides to fit the overall width of the roof coverage. A multiple sided roof maybe a little more complicated to figure. You can consult the manufacturer for hip and valley style roofs as they can be custom cut to any length and roof pitch you desire.
Calculating metal roofing in linear feet can be a useful skill when it comes time to cover that new shed or barn. Understanding the basic sizing for metal roofing depends on the amount of coverage you want to have for the building. All metal roofing can be cut to length. The width on the other hand is your choice. 24-inch-wide material will cover 24 inches but comes 28 inches wide for a two-inch overlap at both seam ends. 36-inch material is the same way, it too has a 2-inch overlap for a total width of 40 inches. Regardless of the width, the material coverage is what counts.
Measure the overall width and length of the roof with the tape measure and record this with the pencil on the paper. In the following example we will be calculating a roof that is 20 feet wide and 25 feet long. It will be a simple shed roof. In other words there is only one slope to the single roof. Multiple roofs, such as a gable roof, can be calculated in the same manner. Just take each section at a time and then add the two values for a total linear footage.
Add 12 inches to the length measurement for an overhang of 6 inches at each end of the roof's top and bottom. Add another 6 inches to the overall width for an overhang of 3 inches for the sides of the roof. The final measurement for the calculation will be a length of 26 feet by 20 foot 6 inches wide.
Convert the width measurement to feet by dividing the 6 inches by 12 inches, since 12 inches are in one foot. This will give you .5 feet. The final width in feet is 20.5 feet. Multiply the width times the length to give you a square footage result. In this case, we will multiply 26 feet times 20.5 feet to give us the result of 533 square feet.
Calculate the total linear feet for the roof for using both the 24-inch wide material and the 36-inch wide material. 24 inches divided by 12 inches is equal to 2 feet and 36 inches divided by 12 inches is equal to 3 feet. First we will calculate the 2-foot wide material. Divide 533 square feet by 2 feet and the result is 266.5 linear feet. Next do the same with the 3-foot material and the result is 177.66 linear feet.
Calculate the number of pieces we will need in both the 2-foot wide material and the 3-foot wide metal roofing. Note that the linear lengths are quite different as in the 2 foot wide roofing we will need 266 feet and 6 inches of linear roofing. While in the 3-foot wide material we only need 177 feet and 8 inches of linear material. The overall length for this roof is 26 feet, so for the 2-foot wide material divide 266.5 linear feet by 26 feet and the result is 10.25 pieces or 11 pieces of metal roofing 2 foot wide by 26 feet long. The 3 foot wide material can be found in the same manner. Divide 177.66 linear feet by 26 feet and the answer is 6.83 pieces or 7 pieces of 3 foot wide by 26-foot long metal roofing material.
G.K. Bayne is a freelance writer for various websites, specializing in back-to-basics instructional articles on computers and electrical equipment. Bayne began her writing career in 1975 and studied history at the University of Tennessee.