Wheel Offset Calculator: Compare Offset, Backspacing and Poke

Wheel Offset Calculator

Enter the width and offset of your current wheel and the one you are thinking of buying. You see how far the new wheel moves out at the fender and in toward the suspension, drawn to scale.

Enter your numbers and press Calculate.

How offset moves a wheel

Offset is the distance from the hub mounting surface to the wheel's centerline, in millimeters. The hub face is bolted to the car and stays put, so a lower offset pushes the whole wheel outward and a higher one pulls it in. A wider wheel adds half its extra width on each side.

Backspacing (in) = (width + 1) ÷ 2 + offset ÷ 25.4

Overall wheel width is the stated width plus about 1 inch, because each bead flange adds about half an inch. Mickey Thompson, Speedway Motors and Discount Tire all use that convention, and so does every calculator on this site.

Backspacing by width and offset

Width	−44 mm	−24 mm	−12 mm	0 mm	+15 mm	+25 mm	+35 mm	+45 mm
7 in	2.27	3.06	3.53	4.00	4.59	4.98	5.38	5.77
8 in	2.77	3.56	4.03	4.50	5.09	5.48	5.88	6.27
8.5 in	3.02	3.81	4.28	4.75	5.34	5.73	6.13	6.52
9 in	3.27	4.06	4.53	5.00	5.59	5.98	6.38	6.77
10 in	3.77	4.56	5.03	5.50	6.09	6.48	6.88	7.27
12 in	4.77	5.56	6.03	6.50	7.09	7.48	7.88	8.27

Backspacing in inches. Full chart in the offset guides.

Common questions

What is wheel offset?

The distance in millimeters from the wheel's hub mounting surface to its centerline. Positive puts the hub face toward the street side; negative toward the brakes.

How do I convert offset to backspacing?

Backspacing = (width + 1) ÷ 2 + offset ÷ 25.4. A 9-inch wheel at +18 mm has about 5.71 inches of backspacing.

Will lower offset make my wheels stick out?

On the same width, yes: every millimeter less offset moves the wheel one millimeter farther out.