Now that you have all the old material off the next step in how to upholster a chair is going to be cutting the new fabric. Since every chair is different the amount of material required will vary. But it’s always better to buy too much then to run out. You will want to lay the new fabric out flat then take the old fabric pieces and lay them down on the new fabric to arrange them so that there is no big gaps between pieces. This will help conserve material. Once you have all the old pieces laid on top of the new fabric you can start to carefully cut out the new pieces. I usually allow for a little extra on each piece since you always trim excess fabric off later. Once you have all the pieces cut we can move on with how to upholster a chair.
If you encountered any cardboard when taking the chair apart you will want to add it back in the same way it came out. If the cardboard is in bad shape you can get new cardboard to replace it. Carefully align all the pieces you took off upside down onto the fabric you cut out. You want to secure one side with a staple to hold things in place. You then want to lay down some fabric glue around the edges but it is a good idea to check the material is the correct size before apply the glue. Then you want to apply another staple to the opposite side to hold things in place. Make sure your fabric is taut and not slack. Repeat this process for the remaining sides. Simply repeat these steps for all pieces being upholstered.