Measure each part of the sofa individually with a tape measure, and record the measurements on a notepad. Areas that need to be measured are the inside and outside of the back, inside and outside of the arms, the front of the arms, the seat and the front gusset. The front gusset is the outside facing area that runs beneath the cushions and connects the armrests. If any part of your sofa is curved, like the back and the arms, measure and record the widest and highest points of each piece to ensure there will be enough fabric.
Add 2 1/2 inches to each measurement to allow room for seams.
Add up the total inches for each measurement, and divide the sum by 36. This will be the number of yards of fabric you will need to reupholster the sofa.