SIZE
The backing should be a minimum of 6 inches wider and 6 inches longer than your quilt top.
This is to allow for the backing to be pinned onto the rollers, to allow supporting at the sides and for some taking up of fabric into the quilt. If in doubt, leave it bigger and I will trim it to size.
JOINS on BACKING
Remove all selvedges
1/2 " (1.5 cm) seam allowance
Use a very narrow zig zag instead of a straight stitch if you have to piece your backing as this will have more 'give'.
Press seam allowance open .
SQUARING
The backing piece needs to be squared off at the top and bottom as it will be attached to roller bars. If the edges are not square, the quilt will be distorted due to the backing fabric being pulled irregularly.
WADDING/BATTING
If you supply your own wadding/batting it should be a minimum of 6 inched wider and longer than your quilt top.
I also have 1.5m & 2.4m wide wadding/batting in stock, usually Matildas Own 60/40 Wool Poly blend which quilts up softer and with a slightly loft than cotton wadding.