How to Measure the Surface Area on a Hip Roof

Draw a simple sketch of the roof that shows one end of the roof as well as one side of the roof. Divide the sketch into triangles and rectangles. Typically, for a hip roof, both ends of the roof are triangles. The sections of the sides consist of a center rectangle with a triangle on either side of the rectangle.

Measure the dimensions of the roof using a ladder and a tape measure. For one end of the roof, measure from the top part of the triangle down the base of the triangle, and then measure the triangle's base. Perform these same measurements on the two triangles on either side of the center rectangle on one of the roof's sides. Measure the length and width of the side rectangle as well.

Find the area of the end triangle by multiplying the base times the height and dividing by 2. Multiply your answer times 2 since you have a triangle on each end of the roof. For example, if the base of the triangle was 30 feet and the height was 15 feet, you would multiply 30 by 15 to get 450. Divide by 2 to get 225 square feet for the surface area of one triangle. Multiply this times 2 to get the surface area for the triangles on both ends of the house, which would equal 450 square feet.

Calculate the area of the triangles on either side of the center rectangle on the side of the roof by using the same formula: (base x height) / 2. Multiply your answer times 4 since there are two triangles on each side of the roof. Assume for this example that the height of a triangle on either side of the rectangular section has a height of 15 feet and a base of 10 feet. In this case, you would multiply 15 times 10 to get 150. Divide by 2 to get 75 square feet for one triangle. Multiply this times 4 to get 300 square feet for the triangles on the sides of the roof.

Determine the area of the rectangular portion of the roof's side by multiplying the length times the width. Multiply this answer by 2 to account for both sides of the roof. In this example, assume that the rectangle is 50 feet long and 15 feet high. Therefore, you would multiply 50 times 15 to get 750. Multiply 750 times 2 to get 1,500 square feet for both rectangles.

Add the individual surface areas of both ends and both sides of the roof to find the total surface area. In this example, you would add 450, 300 and 1,500 to get a total of 2,250 square feet for the surface area of the roof.

Divide your total surface area by 100 if you want to find the squares of shingles required to cover the roof. A square of shingles is equal to 100 square feet. This is a common way to describe the surface area of a roof. For example, if the roof has a surface area of 2,250 square feet, divide this figure by 100 to get 22.5 squares of shingles needed for this roof.