Upholstering Instructions at Better Homes and Gardens. In a nutshell: Strip the chair of its original fabric and use the pieces as pattern. Then pin the pieces wrong sides out onto the chair. Remove pinned cover and sew it together, with welting reinforcing the seams. Put sewn cover back on the chair. It should fit like a glove!
Sewing Projects for The Home - Square Hot Pads with Hand Pocket - Free DIY Sewing Patterns, Easy Ideas and Tutorials for Curtains, Upholstery, Napkins, Pillows and Decor http://diyjoy.com/sewing-projects-for-the-home
I consider myself a bit of a do-it-your-selfer, but after many years and many more failed projects, I have also come to realize my own limits. One of those limits is reupholstery. So, for me the question is not, “how do I reupholster this chair?” it is, “how much fabric should I buy to give to the guy I’m paying to reupholster this chair?”