Measure the wheel’s overall width from outer lip to outer lip
Divide the overall width by 2 to find the centerline
Measure the distance from the hub mounting face to the wheel’s inner edge
Subtract the centerline from the hub mounting face measurement
The result is the rim offset
Positive offset means the mounting face is toward the outer side of the wheel
Negative offset means the mounting face is toward the inner side of the wheel
Zero offset means the mounting face is exactly at the centerline