Disassemble any parts of the chair that block access to the fabric. In a dining chair with only an upholstered seat this mean using a screwdriver to remove the seat. In a full upholstered chair, this means removing cushions and any glued down portions of the chair that are upholstered such as the chair back or arm rests.
Remove the fabric from the chair. The simplest way to get the right size of fabric for your chair is to take apart the existing fabric and use it as a pattern. On a dining chair simply remove the fabric from the seat you just removed. For a full-upholstered chair remove all the fabric from the chair and use a seam ripper to take apart the fabric into individual pieces.
Measure the dimensions of the chair if you prefer not to remove the original fabric. Measure each covered area carefully and add 1/2 to 5/8 inch to each edge to for a seam allowance (where the pieces will be sewn together). Copy these measurements onto newsprint and cut them out so you can use them as a pattern.
Purchase new fabric based on either the measurements you have taken or on the fabric you removed from the chair. A basic rule for fabric requirements is around 3/4 yard of 54-inch fabric will do two chair seats. A wing chair takes around 5 to 7 yards, and a club chair takes about 5 to 6 yards.
Cut out new pieces of upholstery using either the paper patterns you made or the fabric patterns you took off the original chair.
Sew together the pieces of fabric in the same manner as they were previously sewn. Fit them to the chair often as you work so any mistakes can be corrected right away.
Replace any foam or batting that is worn down before putting the new upholstery on. Use 1-inch-high density foam on the seat with an additional layer of bonded polyester batting for a smooth appearance. Foam should be cut slightly larger than the seat (about 1/4 inch all the way around), and the batting should not hang over the edge or it will create a bumpy distortion.
Put the fabric back on the chair once the pieces are sewn together and the foam and batting are in place. Glue any free edges to the frame of the chair to avoid them slipping and messing up the fit. On edges that may possibly be seen, such as the bottom of a dining chair, fold free edges so they are as inconspicuous as possible and cut away any extra fabric.
Staple down the edges you just glued down to make sure they will hold.
Hand sew any edges of the fabric left open, such as an edge of a cushion left open to insert the foam. Reattach seats, chair backs or armrests to finish your re-covering project.