The main steps that need to be taken into consideration when looking at a couch cushion replacement, are taking the correct measurements and having the right equipment and fabric to complete the job. The first item you will need is a sewing machine, you will also need a good pair of scissors, pins, tape measure, paper to draw the pattern on and a marking pen or pencil of some sort to draw the pattern. Next step is to have a look at the cushions you want to replace and decide if it is necessary to replace the foam on the inside. If the foam needs replacing you will have to purchase new foam, you will also need to decide on what fabric you want to cover the cushions with, it should be a heavy type fabric such as the kind used for upholstery, or something that will stand up to a fair amount of wear. If the cushions are going to have a zipper so they can be removed for washing, you will need to purchase one zipper for each cushion and good quality cotton for stitching them together.
Sometimes when doing a couch cushion replacement there may be different sizes, measure the cushions you want to replace and decide how many are the same and how many have a different measurement. If there are two different sizes on the couch, you will need the measurements of one cushion of each size and this will give you two different patterns to work with. Take the measurements of the square or rectangle on the top of the cushion, and also take the side panel measurements. Using the paper you have to draw the pattern on, draw the measurements of the cushions top then draw another line around this cushion top measurement making it about a ½” on the outer edge, as this allows for the seam. Do this with three side panel measurement also allowing for a seam, and do one panel for the back with an extra inch for seam allowance so this panel can be cut in half longwise and the zipper sewn between these two pieces. Mark what each pattern piece is for and how many of each piece you require to complete a cushion.
Once you have the patterns completed, you will need to work out how much fabric will be required. Do this by using the measurements from the patterns and adding these together, plus how many couch cushion replacements there will be and allowing a certain amount for the width of the material as some fabrics are wider than others. When purchasing the fabric, also purchase cotton and zippers of a correct length and of a matching color, as well as pins and scissors if you need them. If the foam needs replacing, you can purchase replacement foam pieces from a supplier, make sure you take the measurements of the foam with you and tell them what you are using it for, as there are different foam firmness ratings. Once you have all the materials and are ready to begin, check your pattern measurements to any newly purchased foam pieces and adjust the pattern if necessary before cutting the fabric. Next put the pattern on the fabric and fix with pins, then cut out the number of each pattern pieces required. Begin sewing by completing the zipper section first, then stitch this and the side panels to the bottom and sew the side and back panel ends together, open the zipper, then stitch the top panel on, then turn the whole piece inside out through the open zipper. You can then insert the foam. Do all the other cushions the same making sure you sew the fabric on the wrong side. Otherwise you may like to have an upholsterer replace them for you.