Wheel Offset CalculatorWheel Offset & Backspacing Calculator — Poke and Clearance
Backspacing (in) = (wheel width + 1) ÷ 2 + offset (mm) ÷ 25.4.
Compare your current wheels with new ones and see exactly how far the new set will stick out (poke) or tuck in, how much inner clearance to the suspension you gain or lose, and the backspacing of each — before you buy.
Current vs new wheel
Current wheel
New wheel
Offset is stamped on the wheel as ET, e.g. ET35. Use a minus sign for negative offset (e.g. −12).
Inner edge moves 0.17″ away from the suspension. Track width changes by about +2.34″.
Check fender clearanceCross-section (top view): hub face at the dashed line
Fitment comparison
| Measurement | Current | New | Change |
|---|---|---|---|
| Width (nominal) | 8.0″ | 9.0″ | +1.0″ |
| Offset | 35 mm | 18 mm | −17 mm |
| Backspacing | 5.88″ | 5.71″ | −0.17″ |
| Front spacing (hub to outer lip) | 3.12″ | 4.29″ | +1.17″ |
How do you calculate wheel offset and backspacing?
Backspacing (in) = (wheel width + 1) ÷ 2 + offset (mm) ÷ 25.4. Lower offset pushes the wheel outward. Going from an 8-inch wheel at +35 mm to a 9-inch wheel at +18 mm moves the outer lip 1.17 in further out (more poke) and the inner edge 0.17 in away from the suspension.
Part of our Tire, Wheel & Gearing calculators — for the core estimate, start with the Tire Size Calculator.
Positive, zero and negative wheel offset
Positive offset (+)
The mounting face is toward the outside of the wheel, tucking it under the fender. Most modern front-wheel-drive and many passenger cars use positive offset.
Zero offset (0)
The mounting face sits exactly at the wheel’s centerline.
Negative offset (−)
The mounting face is toward the inside, pushing the wheel outward for a wider, deep-dish stance common on lifted trucks.
How to compare wheel fitment
Find current specs
Width and offset (ET) are usually cast or stamped inside the wheel.
Enter the new wheel
Use the manufacturer’s listed width and offset.
Read poke and inner change
Positive poke means the outer lip moves out toward the fender.
Check clearance
Test-fit at full steering lock and with the suspension compressed.
Wheel offset and backspacing formulas
Backspacing = overall width ÷ 2 + offset (mm) ÷ 25.4
Front spacing = overall width − backspacing
Poke change = new front spacing − old front spacing
Inner clearance change = old backspacing − new backspacing
Offset (mm) = (backspacing − overall width ÷ 2) × 25.4
Pair the wheel with the right tire height using the Tire Size Calculator, and correct the speedometer with the Speedometer Calibration Calculator if the diameter changes.
Example: 8″ +35 to 9″ +18
| Measurement | 8 in +35 mm | 9 in +18 mm | Change |
|---|---|---|---|
| Backspacing | 5.88 in | 5.71 in | -0.17 in |
| Front spacing | 3.12 in | 4.29 in | +1.17 in |
| Track width (both sides) | +2.34 in |
The new wheel pokes out 1.17 in and gives 0.17 in more room on the inside. These match the calculator’s defaults.
Wheel fitment checklist
- Bolt pattern and center bore must match your hub (or use hub-centric rings).
- Brake clearance: big brakes need enough spoke clearance, not just offset.
- Load rating: the wheel’s rated load should meet or exceed your vehicle’s needs.
- Scrub radius: large offset changes alter steering feel and may increase wear.
- Local rules: some places restrict wheels or tires that extend past the fender.
Lifted tow rig? Re-check payload and GCWR with the Towing Capacity Calculator after adding heavier wheels and tires.
Related calculators
Wheel Offset Calculator FAQs
Add 1 inch to the wheel width, divide by 2, then add the offset in millimetres divided by 25.4. An 8-inch wheel at +35 mm has about 5.88 in of backspacing.
It moves the wheel outward, increasing poke and track width, and moves the inner edge away from the suspension.
Not inherently, but large negative offsets increase scrub radius, leverage on wheel bearings and the chance of rubbing fenders. Many lifted trucks run negative offset deliberately.
How far the outer face of the wheel and tire extends past the fender. More width or less offset increases poke.
At the same offset, about half an inch further out and half an inch further in.
Measure from the hub face to the inside of the fender lip, then choose a width and offset whose front spacing matches that distance minus your desired gap.
Yes. ET is the German abbreviation for offset (Einpresstiefe), given in millimetres.
About the developer
Manzoor Ahmad
Web Designer & Calculator Developer · 13+ years of web development and SEO experienceI’m a professional pharmacist turned tech geek, and I designed and coded this wheel offset calculator myself. Wheel fitment depends on things a calculator can’t see, like brake calipers and fender shape, so the results are framed as changes from your current setup — the most reliable way to compare.
Found a number that looks wrong, or want a feature added? Tell me through my author page — corrections are fixed and re-dated.
Sources
- The Tire and Rim Association — Tire and rim standards
- NHTSA — Tires
- SAE International — J2530: Aftermarket wheels — performance requirements
Disclaimer: Results use nominal dimensions; actual wheel and tire widths vary by brand. Always confirm bolt pattern, center bore, load rating and physical clearance before driving. Not a substitute for a professional fitment check.
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