If you plan to put a new roof on your home, shingles will be just one of the items you will need for the project. Determining how many shingles you will need means you will need to climb onto your roof and measure each area you need to put shingles on. Once you have these numbers in hand, a bit of math will tell you how many square feet of roof you have to shingle. It is only a short step to tell how many squares of shingles you will need and one more short step to tell how many bundles of shingles your project will require.
Use a measuring tape to measure the length of the area to be shingled. Regardless of the type of roof, you will have to climb up to the roof with a ladder. Measure the width of the roof, from the gutter to the ridge of the roof. The ridge is the peak of the roof, where one side stops going up and the other side starts going down.
Use your calculator to multiply the length of the roof by the width of the roof to determine the square footage of the roof. Divide this number by 100 to determine the number of "squares" in that part of the roof. One "square" of roof equals 100 square feet of roof.
Multiply the number of squares by 3. Each bundle of shingles has 33 1/3 square feet of shingles. This means that there are three bundles of shingles per square.