Do a sample test first. I usually use the side of my walking foot as a guide and it is larger than 1/4 inch. You will really need to make the same size sandwich square and try out your binding. Depending on the batt you used and the seam allowance, plus the width of the binding they can all play a role. Nothing I hate worse than getting a binding sewn all around a huge quilt and then not have enough to pull it over and hide the original stitching line.