2 1/4" when using separate binding - sew to the back and pull to the front, machine stitch down. BUT my usual way is to cut the backing 1" bigger than the front - after sandwiched and quilted use rotary cutter and ruler to make backing 1" larger. Fold over just past quilt top, bring to front and sew down. I know this is not the preferred way to do it, but all of my grandmother's are done this way and it works for me.