Measure the back of the sofa from top to bottom at the highest point. Measure from side to side at the widest width. Do the same with the arms, the sides and the front of the couch and the cushions. Record your measurements.
Calculate how many yards total you will need. A yard of upholstery hide always measures 36 inches long and about 50 inches wide. Calculate extra leather for seams where you sew the leather, such as the cushions. About an inch makes a good amount. Where you staple, you will need a few extra inches of fabric so you can grip and pull tightly.
Order your leather---either a full hide or by the yard, depending on your supplier. (A full hide measures about 50 square feet.) Consider ordering extra leather in case you make mistakes or tear the leather during or after upholstery.