Compare a new wheel to your current one before you buy: how much closer it sits to the suspension and how much farther it pokes out toward the fender.
Offset is the distance from the wheel's centerline to its mounting face, in millimeters. Backspacing is the distance from the mounting face to the wheel's inner edge, in inches. The listed wheel width is measured between the bead seats, and the lips add about half an inch per side, which is where the extra inch comes from.
A wider wheel adds width to both sides unless the offset changes to shift it. This calculator shows the result on each side so you can check it against the room you've measured.