Take measurements to determine the size of the piece of fabric you’ll need to cut.
Measure around the box and add 1/2 inch for fit + 1 inch for seam allowance. This will be the length of fabric you’ll need to cut for the body of the cover.
Now measure from the top edge of the box to the bottom then multiply times 2 and add 1 inch for seam allowance. This is the width of the strip of fabric you’ll need to cut.
My box measured 18 1/2 around and 5 1/4 high so I needed a strip of fabric that was 20 long by 11 1/2 wide.