Wheel Offset & Backspacing Calculator
Convert between wheel offset (ET), backspacing, and centerline position to predict how a wheel will sit relative to the hub and fender.
Results
What is it?
Wheel offset (ET, from German "Einpresstiefe" = insertion depth) is the distance in mm from the wheel's mounting face to its geometric centerline. Positive ET pushes the wheel inward; negative ET pushes it outward (creating "poke" or "stance"). Backspacing is the distance from the mounting face to the inner lip, measured in inches.
How to use
Enter your wheel width in inches, the ET offset in mm (found stamped on the back of the wheel), and your vehicle's hub flange thickness. The calculator converts between ET and backspacing, and shows the wheel centerline position � essential for checking inner clearance to suspension components.
Example scenario
A 9-inch wide wheel with ET35 and a 70 mm hub flange: wheel width in mm = 228.6 mm, centerline = 114.3 mm. Backspacing = (114.3 + 35 + 70) / 25.4 = 8.63 inches. If going from ET35 to ET20 on the same wheel, the wheel moves 15 mm outward � check for fender clearance.
Pro tip
A useful rule: each 5 mm reduction in ET moves the wheel 5 mm outward and inward simultaneously (the wheel pivots around the hub). Check both fender clearance at the outer lip AND suspension/caliper clearance at the inner barrel before ordering wheels. Many fitment databases (e.g. Fitment Industries) list safe ET ranges per vehicle.