Measure the cushion from the seam at the back of the seat to the seam at the front. Double that number and add 1 inch to get the length of fabric you will need to cover the top and bottom of the cushion. Adding 1 inch gives you a 1/2-inch seam allowance on each end of the cushion.Click to see full answer. In respect to this, how much fabric do I need for cushions?For a cushion inner 45cm x 45cm, the actual size of the cushion cover should be around 42.5cm x 42.5cm. One metre of standard width (137cm) furnishing fabric is enough for three plain cushions with either zip or standard button fastening to fit up to 45cm x 45cm size. Other styles of cushion will need more fabric. how much fabric do I need to make a bench cushion? A standard seam allowance is 1.5 cm or 5/8″, which is how much we used. If it makes math easier, you can make a 1/2″ seam allowance. Just make sure to add this measurement onto both sides of each piece you cut out. For the size of cushion we were making, we needed 1 1/4 yards of 60″ width upholstery fabric. Simply so, how do you measure fabric for seat cushions? Measure the length of the top of the chair pad from the front to the back of the chair. Add an additional 1 inch for a 3/8-inch seam allowance on each end. Double that number for the top and bottom of the chair. For example, if the chair length is 20 inches, add 1 inch for the seam allowance and then multiply by two.How do I calculate how much fabric I need? Figure out how much fabric you need with this formula: Width of fabric divided by width of one piece equals the number of pieces that fit into width (rounded down to the whole number). Total number of pieces divided by number of pieces that fit into width equals number of rows you need.