Convert advertised wheel offset (ET, mm) to measured backspacing (inches) and back, including the industry 1" flange allowance — free, private, in-browser.
Advertised bead-seat width (inches).
8"
Rim width
45 mm
Offset
6.27"
Backspacing
9"
Overall width
Overall width includes the industry 1" flange allowance (bead-seat to overall).
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Advertised wheels use offset in millimetres (ET). Measured wheels on a bench use backspacing in inches. Convert either way once you know rim width: that is the translation between a catalog ET35 and a tape measurement from the inboard flange.
Overall width used in the math is rim width plus 1 inch of flange, the usual aftermarket convention. Backspacing = overall/2 + offset(mm)/25.4; the inverse recovers ET. If your wheel has an unusual lip, the tape and the catalog can still disagree by a few millimetres.
Outputs include width, ET in mm, backspacing in inches, and overall width in inches so you can cross-check a listing. Direction Offset→BS or BS→Offset keeps you from solving the wrong unknown. Ranges cover typical passenger and light-truck wheels (about 3.5–16" width, −80 to 120 mm ET).
No account and no upload. This is geometry on one wheel, not a vehicle fitment check. For how a width or ET change moves poke and tuck versus your current wheel, use Wheel Offset Calculator. Close the tab and the millimetres are gone.
Use Offset→BS when you have a catalog ET. Use BS→Offset when you measured the inner face with a straightedge.
The advertised width between flanges, in inches (for example 8 or 9). Width is required both ways.
ET can be negative (deep dish). Backspacing is typically a few inches on passenger wheels. Stay inside the field ranges.
Confirm the 1" flange assumption matches how you measured. Then check poke/tuck on Wheel Offset if you are changing from a known wheel.
Straight answers on privacy, limits, and how the workspace behaves.
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