Wheel Offset / Backspacing Calculator

Convert between offset (mm) and backspacing (in). Useful when shopping wheels listed in one convention while your fitment notes use the other.

How it works

Backspacing is measured from the wheel's inner mounting face to the rear edge of the wheel barrel. Offset is measured from the wheel's centerline to the mounting face. The two describe the same geometry from different reference points:

backspacing (in) = width / 2 + offset (mm) / 25.4 + 0.5

A higher (more positive) offset pushes the wheel face outward toward the fender; a lower (or negative) offset pulls the wheel face inward, increasing dish and poke.

Examples

  • 9.5" wheel, +15mm offset → 5.84" backspacing
  • 10" wheel, -25mm offset (deep dish) → 4.52" backspacing
  • 8" wheel, +0 offset → 4.50" backspacing

Disclaimer

Estimates only. Real fitment depends on coilover height, camber, tire model, fender modifications, and wheel construction. Always physically test-fit before final installation.