What is wheel offset (ET)?

Offset is the distance in millimeters from the wheel’s centerline to the mounting pad. Positive offset puts the pad toward the street side of the centerline (wheel sits more inboard). Lower or negative offset moves the wheel outboard — more poke.

What is a wheel fitment calculator?

A wheel fitment calculator compares stock and new rim width and offset so you can see poke, tuck, backspacing, and approximate track change before you buy. This page is built for that job — pair it with a tire size check and bolt-pattern match so diameter, PCD, and ET all clear together.

How do you calculate backspacing from offset?

Backspacing (inches) = rim width ÷ 2 + offset (mm) ÷ 25.4. Frontspacing is rim width minus backspacing. Backspacing is the distance from the mounting pad to the inner lip — useful when checking fender and suspension clearance.

Will these wheels fit my car?

Geometry gets you most of the way: match bolt pattern and hub bore (or use hub-centric rings), keep overall tire diameter near stock, and compare width/offset so the inner lip clears struts/control arms and the outer lip clears the fender. This tool shows the width and ET delta; you still need to verify real clearance on lock and over bumps.

Does a lower offset always mean more poke?

For the same rim width, yes — dropping offset moves the mounting face and outer lip outboard. Wider wheels also change front- and backspacing even at the same offset, so compare both width and ET when plus-sizing.

Why is offset always in millimeters?

Wheel manufacturers stamp ET (Einpresstiefe) in millimeters worldwide. Rim diameter and width are still commonly listed in inches. This calculator keeps offset in mm and converts width/diameter with the in/mm toggle.

What about tire width and track?

Optional tire section widths estimate how total track changes when both sides match the new setup. Geometry is approximate — real clearance also depends on fender roll, camber, and suspension travel.

Wheel Offset & Backspacing Calculator

Compare stock and new wheel width and offset — backspacing, face poke, and optional tire track delta for fitment.

Compare stock vs new rim width and offset — backspace, poke, and track delta.

Stock wheel

OEM size and ET from the door sticker or wheel stamp. Offset is always millimeters.

Diameter (in)

Width (in)

Offset (mm)

New wheel

Aftermarket plus-size defaults: 18×9.5 ET+22 — override with your quote.

Diameter (in)

Width (in)

Offset (mm)

Tire section (optional)

Add section widths for an approximate track / scrub estimate.

Include tires

Fitment bay · hub-referenced section

Pad fixed · rim moves with ET & width

More poke

Δ offset

-13

mm · face outboard 13 mm

Stock
17×8
ET 35 · BS 5.38 in
New
18×9.5
ET 22 · BS 5.62 in
Inner lip
+0.24 in
vs stock (inboard)
Outer lip
+1.26 in
vs stock (outboard)

Approx. track change +26 mm (both sides)

Wheel offset, backspacing, and poke

Offset (ET) is millimeters from the rim centerline to the mounting pad — stamped on nearly every modern wheel.
Backspacing (in) = width ÷ 2 + offset ÷ 25.4; frontspacing is the rest of the rim toward the street.
Lower offset or a wider rim usually means more poke — check fenders, tie rods, and strut clearance before you buy.

Plus-sizing a wheel is rarely just a diameter jump. Move from a stock 17×8 ET+35 to an 18×9.5 ET+22 and the mounting face, inner lip, and outer lip all shift relative to the hub. This free wheel offset calculator turns width and ET into backspacing and frontspacing, then shows how far the new setup sits inboard or outboard versus OEM.

Enter stock and new rim diameter, width, and offset in millimeters. Diameter is optional for the core geometry but keeps the comparison readable. Toggle inches and millimeters for rim dimensions; offset stays in mm because that is how wheels are sold. Optionally add tire section widths for a rough track change estimate when both sides match the new package.

Treat the numbers as geometry, not a guarantee of zero rub — camber, fender liners, and load still matter. Pair this with the tire size calculator for overall diameter, and a bolt pattern check before you order.

Wheel fitment checklist (offset, tires, and bolt pattern)

“Will these wheels fit?” is really three questions: bolt pattern and hub bore, overall tire diameter, and where the rim sits in the arch. This wheel fitment calculator answers the third — width and ET versus stock — so you can see poke, tuck, and backspacing before you click buy. Match PCD with the bolt pattern finder, keep rolling diameter near OEM with the tire size tool, then use the offset delta here to decide if you need a spacer, a different ET, or a fender roll.

Common plus-size traps: going wider at the same offset pushes the inner lip toward the strut, and dropping ET at the same time adds outer poke into the fender. Lowered cars and trucks with big AT tires are least forgiving. Recheck both sides of the rim, not just the face you see from the street — backspacing is what hits uprights and tie rods.

How to use the wheel offset calculator

Enter the stock wheel. Use the OEM diameter, width, and offset (ET in mm) from the door sticker, wheel stamp, or parts catalog.
Enter the new wheel. Plug in the aftermarket size and offset you are considering — diameter is optional for the offset math but helps label the comparison.
Read fitment delta. Check Δ offset, backspacing, and whether the face moves outboard (poke) or inboard (tucked). Add tire section widths if you want an approximate track change.

Wheel Offset & Backspacing Calculator

Wheel offset, backspacing, and poke

Wheel fitment checklist (offset, tires, and bolt pattern)

How to use the wheel offset calculator

Wheel offset and fitment FAQ

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