Measure the height and width of each surface on your couch -- front, back, seat, arms. Include areas such as the front of the arm, the inside and outside of the arm and the skirt, if your couch has one. Measure each section at its widest point for the best yardage accuracy. Write these measurements down.
Measure the length, width and height of all cushions. If a cushion has a T shape, measure it at the widest point of the T. Write these measurements down.
Measure the length and width of any throw pillows. Multiply the length by 2. Write these measurements down.
Multiply all of the measurements for the couch arms by 2.
Add 2 inches to all of these measurements for seam allowance.
Add these measurements together.
Divide that number by 36.
Add 2 to 3 yards to this new number if you are using a patterned fabric to allow for pattern matching.
Add 1 to 2 yards if you plan on using welting or piping on your couch.
Add 2 to 3 yards if your couch has -- or if you plan on including -- a skirt.