Wheel Offset Calculator

Offset is the distance from a wheel's mounting face to its centreline in millimetres, and backspacing is the same fact measured from the inner lip in inches. This tool converts either one into the other from the wheel width, and the third mode takes the wheel on the car and the wheel you are thinking of buying and reports how many millimetres the outer and inner edges each move. The conversion adds an inch to the stamped width for the half inch of flange on each side, which is the trade convention. Comparisons use the stamped width alone, since the flange is the same on both wheels and cancels. The figures say where the wheel sits, not whether it clears the strut, the caliper or the arch, and only a test fit settles that.