Remove the wheel from the vehicle
Lay the wheel face down on a flat surface
Measure the overall wheel width from bead seat to bead seat
Divide the wheel width by 2 to find the centerline
Measure the mounting pad distance from the back edge of the wheel to the hub mounting surface
Subtract the centerline measurement from the mounting pad distance
Positive result = positive offset
Negative result = negative offset
Zero result = zero offset
Use a straightedge and ruler for more accurate measurement
Confirm measurements in millimeters