The first step in upholstering a sofa is figuring out how much fabric you need. This can be tricky, since there are many different styles of sofas and cushions. There are also many styles of upholstery fabric. In general, plain fabrics and fabrics with small prints will require less yardage than fabrics with stripes (especially wide stripes) or large floral prints. That's because the pieces for stripes and prints have to be cut so that the pattern matches up with the pieces next to it, which can take extra fabric. For a large print or stripe, add 10 to 15 percent to guidelines given below.
Measure the width of the back of the sofa at the widest point. (For example, 7 feet 7 inches.)
Measure the height of the back of the sofa from the lowest point of the upholstery to the highest point on the back of the sofa. (For example, 2 feet 2 inches.)
Measure the depth of the sofa by measuring the widest point of the side. (For example, 2 feet 6 inches.)
Round all your measurements up to the nearest half foot. (For example, 7 feet 7 inches would be 8 feet, and 2 feet 2 inches would be 2 1/2 feet.)
Multiply the three measurements together. (For example, 8 x 2.5 x 2.5 = 50.)
Multiply this number by 0.35 for a sofa with loose cushions on the back and reversible seat cushions (for example, 50 x 0.35 = 17.5), or multiply by 0.25 for a sofa with attached back cushions and reversible seat cushions. This is the number of yards you need. Use a table, such as the one listed in Resources below, to find the number you need to multiply by for other types of sofa styles and sizes.
Multiply the number from Step 5 by 0.04 to find the yardage for a sofa skirt up to 7 inches tall or 0.08 for a soft skirt up to 12 inches tall. (For example, 50 x 0.04 = 2 yards.) Add this amount of yardage to your total.