- Measure the length and width of all the surfaces on your roof in feet. Write down each length and width on a piece of paper.
- Multiply each length and width in any order you want. Write the surface area in square feet next to each item on your list. Add all the areas together to get the total roofing surface area.
- Divide the total area by 100 and multiply it by 3. Buy this number of bundles of shingles. Be sure to add about 10 percent extra to the bundle number to account for breakage and other accidents.
How to Calculate to Shingle a Roof
As with any other home improvement project, purchasing enough materials to properly install a shingled roof is essential. The amount of shingles you need depends on the surface area of your roof. To avoid taking unnecessary trips to the hardware store, buy more shingles than you need for your roof. This will help account for accidents where you drop a shingle and will cover replacing any broken shingles that you might discover in the bundle.