Wheel Offset Calculator
Calculate wheel offset in millimeters from a wheel's width and backspacing measurement. Used when fitting aftermarket wheels to ensure correct clearance with suspension and bodywork.
About this calculator
Wheel offset is the distance between a wheel's hub mounting surface and its centerline, expressed in millimeters. The formula is: Offset = Backspace − (Wheel Width / 2), where all measurements are in inches and the result is then converted to millimeters (multiply by 25.4). A positive offset means the mounting surface is toward the outside (street face) of the wheel, pushing the wheel inward toward the suspension. A negative offset means the mounting surface is inward, pushing the wheel outward — common on lifted trucks and off-road vehicles. Zero offset places the mounting surface exactly at the wheel's centerline. Getting offset right is critical: too much positive offset can cause tire rubbing on the strut; too much negative offset can stress wheel bearings and cause the tire to protrude past the fender.
How to use
Suppose a wheel is 9 inches wide and has a backspacing of 5.5 inches. Step 1: Halve the wheel width: 9 / 2 = 4.5 inches. Step 2: Subtract from backspacing: 5.5 − 4.5 = 1.0 inch of offset. Step 3: Convert to millimeters: 1.0 × 25.4 = +25.4 mm offset. This positive offset means the mounting face sits 25.4 mm outboard of the wheel's centerline, positioning the wheel slightly inward — typical for many passenger cars and light trucks.
Frequently asked questions
What is the difference between wheel offset and backspacing?
Backspacing is the physical distance in inches from the back rim lip of the wheel to the hub mounting surface, measured with a ruler. Offset is a derived value in millimeters that expresses how far the mounting surface deviates from the wheel's true center. Backspacing is easier to measure on a physical wheel, while offset is the standardized specification used by manufacturers. You can convert between them once you know the wheel's width, which is exactly what this calculator does.
How does wheel offset affect vehicle handling and tire clearance?
Offset changes the scrub radius and the effective track width of the vehicle. A more negative offset widens the track, which can improve lateral stability but increases stress on wheel bearings and may cause tires to rub on fender lips. A higher positive offset narrows the effective track and pushes the tire toward the suspension components, risking contact with the brake caliper or strut during full lock steering. Staying within ±10 mm of the OEM offset is generally safe for street use without modifications.
What offset do I need when switching to wider aftermarket wheels?
When fitting wider wheels, you typically need to reduce the offset (go less positive or more negative) to keep the tire's centerline in approximately the same position as the original wheel. For every extra inch of width added to the wheel, the offset should decrease by roughly 12.7 mm to maintain the original fitment geometry. Always verify clearance at full steering lock and over suspension compression with spacers or test-fitting before finalizing a wheel and tire combination.