Wheel Offset & Backspacing Calculator
Convert ET offset to backspacing and estimate poke & inner clearance changes.
REAL-WORLD EXAMPLE
You’re considering 18x9.5" wheels with +35mm offset on a car that originally came with 18x8.5" +45mm wheels. Compared with your stock setup, the new wheels will sit roughly 0.9" (about 23mm) further out toward the fender and the inner barrel will move about 0.1" (a few millimetres) closer to the suspension. The calculator below shows these changes more precisely so you can judge whether you’ll still clear struts, control arms, brakes and fender lips.
Width is measured between tire bead seats. We add ~1" internally to approximate total lip-to-lip width when converting to backspacing.
Measure from the inner wheel lip (rear edge) to the mounting face.
Offset
+25.4mm
Wheel Width
8.0"
Backspace
5.50in
Offset
+25.4mm
Positive — typical OEM fitment
Formula: Offset = (Backspacing − (Wheel Width + 1) ÷ 2) × 25.4 = (5.50 − 4.50) × 25.4 = 25.4mm
Calculations use a 1" flange correction to approximate total wheel width. Actual lip-to-lip dimensions can vary slightly by wheel design.
Typical OEM Wheel Specs by Vehicle Type (Approximate)
| Vehicle Type | Width (in) | Offset (mm) | Examples |
|---|---|---|---|
| Compact / Economy | 6.0–7.0 | +38 to +55 | Honda Civic, Toyota Corolla |
| Mid-size Sedan | 7.0–7.5 | +35 to +45 | Toyota Camry, Honda Accord |
| Performance Coupe | 8.0–9.5 | +30 to +45 | Mustang GT, BMW 3-Series |
| Full-size SUV | 7.5–9.0 | +25 to +45 | Tahoe, Expedition |
| Light Truck / 4×4 | 8.0–10.0 | −18 to +20 | F-150, Tacoma lifted |
| Euro / VW / Audi | 7.5–8.5 | +35 to +55 | Golf, A4, Passat |
AI Insight
Powered by AIGet a plain-English explanation of your results — what they mean for your vehicle and driving experience.
Common Offset Examples (Illustrative)
| Offset (ET) | Backspace (approx.) | Effect | Outer Poke vs +45mm |
|---|---|---|---|
| +45mm | ≈ 6.5" | Typical OEM / conservative | Baseline (stock position) |
| +35mm | ≈ 6.1" | Mildly more aggressive | Wheel ≈ 0.4" further out vs +45mm |
| +25mm | ≈ 5.7" | Aggressive street fitment | Wheel ≈ 0.8" further out vs +45mm |
| +15mm | ≈ 5.3" | Very aggressive / stance | Wheel ≈ 1.2" further out vs +45mm |
| 0mm | ≈ 4.7" | Maximum poke (deep dish look) | Wheel ≈ 1.8" further out vs +45mm |
Backspacing and poke examples above assume a fixed wheel width and are for illustration only. Use the calculator with your exact width and offset to get values tailored to your setup.
How to Use This Calculator
- Measure or look up your current wheel width (inches) and offset (ET, in millimetres).
- Enter your current wheel specs and the new wheel specs you are considering.
- Click 'Calculate' to convert offset to backspacing and see how far the inner and outer lips move relative to stock.
- Review backspace, outer poke, and inner clearance change, then compare with your fender and suspension clearances.
- Use the visual diagram and safety notes on this page as guidance and always test-fit wheels on the actual vehicle before final installation.
Offset & Backspace Formula
About Wheel Offset, Backspacing & Fitment
What Is Wheel Offset and Why Does It Matter?
Wheel offset is the millimetre distance from the wheel’s mounting surface to its centreline. It largely determines how far in or out the wheel sits in the arch. Too much positive offset tucks the wheel deeply under the car and can cause inner rubbing on struts or control arms, while too little (or negative) offset pushes the wheel out, increasing track width and poke but risking fender contact and extra stress on wheel bearings and suspension components.
Backspacing vs Frontspacing (Outer Lip)
Backspacing measures from the mounting pad to the inner wheel lip and is popular in off-road and truck applications. Frontspacing (or outer lip distance) is the counterpart on the outside. Converting between offset and backspacing lets you compare wheels from different catalogs and predict clearance to both suspension and bodywork. Together with tire size and alignment, these measurements define whether a fitment will be tucked, flush, or poked.
Planning Safe and Aesthetic Fitment
Use this calculator to model how new wheels will sit compared to your factory setup before you buy. Start close to OEM offset and width, then adjust gradually while watching inner clearance and outer poke. If you want a more aggressive stance, plan for supporting changes such as camber adjustment, fender rolling, or wider arches, and keep in mind that even a few millimetres of offset change can have a noticeable impact on both look and safety.