What this is

Fitment Calculator is an independent engineering workspace for people making wheel and tire decisions, from first-time buyers to experienced enthusiasts. Its purpose is to make measured changes understandable and to keep every assumption visible.

What it is not

  • It is not a vehicle database and does not know what fits your car.
  • It is not affiliated with wheel, tire or vehicle manufacturers.
  • It does not certify safety or legal compliance.

How to use the calculators

Enter tire sizes and wheel measurements to compare nominal dimensions, wheel-edge movement and theoretical speedometer effects. Results explain the size and direction of a change, with worked examples and limitations.

The calculator directory contains nine focused tools for wheel and tire comparisons, offset and backspacing, spacers, tire dimensions, plus sizing and size conversion. Calculations do not require an account or vehicle-specific personal information.

Where to read more