Flagstone provides a clearly-defined walkway or patio area while maintaining a natural look. Stone is an attractive and durable alternative to concrete, which can crack or spall, creating potential hazards and expensive repairs. Estimating how much flagstone you'll need for your project is one of the first steps you'll take in deciding whether flagstone is the right alternative for you. If you're having trouble, feel free to take a sketch of your plans to the stone supply store and ask for help; stone suppliers know their business and will be able to help you determine how much stone you need.
Ask an assistant to hold one end of a measuring tape at one end of the area to be paved. Extend the tape to one end of the area to be paved and note the measurement. Do the same thing in the other dimension.
Multiply the length by the width to find the area of the space to be covered with stone. If the length of the patio was 8.5 feet and the width was 7.75, you'd multiply those numbers to come to 65.88 square feet. To account for sizing and waste, add 10 to 15 percent to your square footage. In this example, 65.88 x 1.15 = 75.76 square feet.
Choose the thickness of your flagstone. This will depend on your base. If you're installing flagstone over concrete, the stone can be thinner--a half to 1.5 inches. If you're laying the stone over a sand base, it should be 1.5 to 4 inches thick to prevent breaking. If you're not sure what thickness to get, discuss your options with a knowledgeable employee at the stone supply store.
Use the following chart to determine your coverage.
Two thousand pounds of stone will cover: 400 square feet if the stone is a half-inch thick 200 square feet if the stone is 1 inch thick 150 square feet if the stone is 1.5 inches thick 100 square feet if the stone is 2 inches thick 75 square feet if the stone is 3 inches thick 50 square feet if the stone is 4 inches thick
If you chose to use 2-inch thick stone in the example, you would divide the square footage needed by the coverage in the above guide: 75.76/100 = .7576. Multiply that number by 2000 to get the amount of stone needed: 1,515 pounds of flagstone.