Wheel offset calculator (ET)
Before fitting new wheels, enter the current and new rim width and offset to see how each edge moves compared with the current wheel.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter current rim width, current offset et, new rim width and new offset et.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Mounting face to outer edge = width × 25.4 ÷ 2 − ET; to inner edge = width × 25.4 ÷ 2 + ET. Change = new wheel value − current wheel value.
Example
Inputs: Current rim width = 7 in, Current offset ET = 45 mm, New rim width = 8 in, New offset ET = 35 mm. Result: Outer edge change (positive means out toward the fender): 22.7 mm; Inner edge change (positive means closer to the suspension): 2.7 mm; Rim width change: 25.4 mm.
Limits and caveats
- Figures are for the rim only; a wider tire can bulge past the rim edge and change real clearance.
- The tool cannot know the space available on your car, so measure it before buying.
Questions about this tool
What does ET mean?
ET is the offset in mm: the distance from the wheel's mounting face to its centerline. A lower number pushes the wheel further out.
Can ET be negative?
Yes. The mounting face sits inboard of the centerline, so the wheel sticks out a lot, which is common on modified 4x4s.
Do wheel spacers change offset?
Yes. A 10 mm spacer lowers effective offset by 10 mm, so subtract its thickness from the new ET before calculating.