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?"
A good — re: expensive — upholsterer will, of course, gladly give you this information after sending a professional mover to carefully pack and remove your piece of furniture to his workshop. But if you are on a budget, then a lot of this negotiation usually takes place over the phone before you drive the chair over yourself. Even if the upholsterer gives you a general idea of the yardage required, it's good to be able to corroborate that information.
If you're going the low-budget route, then you're probably also purchasing your own fabric at a large fabric warehouse (that's where all of my upholstery fabric has come from!).
So do yourself a favor and print out one (or more) of these handy yardage charts to keep in your wallet or bag so you'll never be stuck clutching the last four yards of an amazing designer fabric and wondering if you really need five.