This is a great project for learning how to put in an invisible zip.
Plus it’s useful for home décor. If you have a particular cushion in mind use those measurements but only add 1cm for seam allowances as you don’t want your cover to be baggy.
 
What you will need:
Two squares of fabric
Matching thread (although I usually use white)
Pins
Sewing machine- with an invisible zipper foot (BE CAREFUL THIS IS DIFFERENT TO A ZIPPER FOOT)
Fabric scissors
Zip 40 cm for a 45 cm cushion.
 
 
By PDFs are available in English and French. Please be aware this a instructions only