Backing must be 8 inches wider and longer than the quilt top. If your quilt is 50" x 50" then your backing should be at least 58" x 58".
Binding should be 2 inches wide, pieced with a 45 degree seam and left flat (don't fold in half and iron). To calculate binding requirements add the length of all 4 sides and divide by 40. The result is how many 2" width of fabric strips to piece together.
For a 60" x 70" quilt the formula is; 60 + 60 + 70 + 70 = 260. 260/40 = 6.5. You will need (7) 2" strips width of fabric.
Backing must be 8 inches wider and longer than the quilt top. If your quilt is 50" x 50" then your backing should be at least 58" x 58".