GarageCalcs: The Grease-Stained Gearhead for the Weekend Wrencher
Meet the Calcs Family →

Wheel offset and backspacing calculator

Compare a new wheel to your current one before you buy: how much closer it sits to the suspension and how much farther it pokes out toward the fender.

Enter your numbers
Current wheel
Positive moves the wheel in, negative pushes it out.
New wheel

Inner clearance change

–
–
Outer position change
–
Current backspacing
–
New backspacing
–
New front spacing
–

Measure your clearance first

Before changing wheels, measure from the current wheel's inner edge to the nearest suspension part and from the outer edge to the fender lip. Compare those to the changes shown here.

Offset and backspacing

Overall width ≈ wheel width + 1 in
Backspacing = overall width ÷ 2 + offset (mm) ÷ 25.4

Offset is the distance from the wheel's centerline to its mounting face, in millimeters. Backspacing is the distance from the mounting face to the wheel's inner edge, in inches. The listed wheel width is measured between the bead seats, and the lips add about half an inch per side, which is where the extra inch comes from.

A wider wheel adds width to both sides unless the offset changes to shift it. This calculator shows the result on each side so you can check it against the room you've measured.

Frequently asked questions

What's the actual difference between offset and backspacing?

Offset measures the distance from the wheel's true centerline to the mounting surface (and can be positive or negative), while backspacing measures from the mounting surface to the back edge of the wheel — they describe overlapping information but from different reference points, which is why both terms show up in wheel specs.

Why does a lower (or more negative) offset push the wheel out?

A lower offset moves the mounting surface closer to the wheel's inner edge, which pushes more of the wheel's width outward past the hub — that's why lower-offset wheels tend to poke out further toward the fender, sometimes requiring fender work to clear.

Why compare a new wheel to my current one instead of just checking specs?

Raw offset and backspacing numbers don't immediately tell you how much clearance actually changes — comparing directly against your current, already-fitting wheel translates those numbers into a real answer: how much closer to the suspension and how much farther toward the fender the new wheel will actually sit.

More Wheels & Tires calculators

Plus-Size Tire Calculator Tire Size Calculator

Read the guide

Choosing Wheel Offset and Backspacing

All GarageCalcs tools