Quilt backing guide
When a quilt backing answer changes after you choose 42, 44, 54 or 108-inch fabric, that is not a bug. Width affects the number of panels, where seams fall and how much length you buy.
42 / 44 in
Often requires panels for larger backs. A cut plan matters as much as the total length.
54 in
Can reduce panels for some sizes; verify the actual usable width rather than assuming it.
108 in
May simplify a backing, but the finished size and extra allowance still determine the cut.
A transparent calculator should tell you which width it used and how the panel layout changes when you switch widths. That is the standard YardageWise is validating before launch.