Stretch your fabric tape measure across the arc of each section of your couch: the back, each arm, each cushion, the front area and the front facing piece of each arm. Be sure to take both the width and length measurement of each section, and then multiply the two numbers together to get the total area of each section. For removable cushions that you will need to upholster on all sides, make sure you measure the top, bottom and sides of each cushion as well. Record all of your measurements in inches.
Add up all of your totals. Add an extra 2 ½ inches for each seam in the couch; since the seams fold under during sewing, you need extra fabric to cover them.
Divide the number of inches by 1,296, the number of square inches in a yard, to get a good estimate of the total number of square yards of fabric needed for your couch.
Add an extra 2 to 3 yards to your measurement to allow for any mistakes in measurement or accidents that may occur while cutting or sewing. It is better to have extra fabric than to run out of matching fabric and have to use mismatched material.
Add an extra 2 to 3 yards of fabric if it has a pattern, in order to allow for matching the pattern on your couch on adjacent sections.