For each cover you will need fabric yardage for the top and lining large enough to cover your chair seat or back plus an additional 10 - 12 inches width and length. (I chose a white cotton denim fabric for my lining because it would be sturdy). Thread, elastic cording, newsprint or other large paper for making a pattern.
Place a sheet of newspaper over the pad on your chair that you want to cover. Use a pencil or pen to trace the outline of the edge of the seat. Fold your pattern in half to make sure it is fairly symmetrical and make any corrections needed. Next, measure the height of your seat pad and decide how far you want the cover to go under the pad. (My seat is about 2 inches thick and I wanted my pad to come in about 1 1/2 inches) Add these figures together and add another 1/2 inch for your seam. (For mine - 4 inches) Trace around your original pattern, adding this extra amount all around. Remember to take into account that your elastic band will have to draw all of this fabric in around the bottom of your pad - that is why I only made a small overlap for my seatback, otherwise it would have been very bulky because of the denim backing.
Use the newspaper pattern to cut out your top and lining pieces.
Sew a 1/2 inch seam allowance all the way around your cover to create a casing for your elastic band. Stitch all but 1 inch of the opening you left for turning as well.
Now you can thread your elastic through the casing. I like elastic cording because it tends to keep its stretch well for this type of application, plus you can use a cord lock to make it more adjustable. I had salvaged the cording and elastic from the bottom edge of a jacket and it was perfect for this job. To thread your elastic through the casing you can use a large safety pin, an EZ threader (this is what I used) or a bodkin. Depending on what kind of elastic and fabric you use this might be a bit of a job, but persevere - it's worth the results!
Once you have your elastic completely through the casing pull it snugly, pin it together and try it on your seat. Adjust to where it hold firmly, then either use a cordlock to hold the ends of the elastic in place, or sew the ends of your elastic together. If you are sewing the elastic, do an extra good job of it because you don't want it to pull out! (Then you can sew up the remaining opening for a neat finished look) After adding the cordlock to mine, I cut the ends of the elastic and sewed them together with a bit of leftover fabric to cover the ends so they won't fray and look shabby.
For the seat back, I left the opening at the bottom.
I think these slipcovers will wear quite well, and it will be nice to be able to launder them if needed. This technique can be used on a variety of chairs and barstools - it's easy to do and can give an outdated piece of furniture a new look with a minimum of time and effort. Best of all, I didn't have to spend any money on my chair makeover because I had all the supplies on hand!