Wheel Offset Calculator

Wheel & hub measurements

Offset (ET) = hub-to-mounting-face distance − half the wheel width (converted to millimeters). Measure hub-to-mounting-face by laying the wheel face-down and measuring from the hub's mounting surface to a straightedge across the wheel's back lip.

Measured overall wheel width (in)

Hub-to-mounting-face (mm)

Wheel offset (ET)

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Enter wheel width and hub-to-mounting-face distance to see the offset.

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Offset (ET)

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Polarity

Enter wheel width and hub-to-mounting-face distance to see what this offset means.

4 min read 4 steps 7 terms 2 examples 6 FAQs ET = hubFace − (width × 25.4 / 2)

Wheel offset — often stamped as "ET" followed by a number — determines how far a wheel sits toward or away from the vehicle's suspension and fender.

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Walk-through

How to Use This Calculator

4 steps

Measure the hub-to-mounting-face distance

Lay the wheel face-down on a flat surface. Place a straightedge across the back lip of the wheel (the barrel), then measure from the straightedge down to the wheel's hub mounting surface — this is the hub-to-mounting-face distance, in millimeters. Enter it above.

Enter the measured overall wheel width

Measure overall measured overall wheel width from the outer rear flange edge to the outer front flange edge. Enter this measured width in inches, not the stamped nominal bead-seat width. Flange projection varies; do not assume the stamped width is overall width.

Read the offset (ET) and its polarity

The hero result shows the calculated offset (ET) in millimeters, with a positive or negative sign. The Positive vs Negative tab explains what that sign means for how the wheel sits relative to the fender.

Compare two offsets to see the fit change

On the Offset Change Effect tab, enter a current offset and a new offset (e.g. when comparing a stock wheel to an aftermarket wheel) to see how far the wheel shifts in or out, and the resulting change in track width.

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Reference

Formula & Methodology

2 formulas

Offset (ET) from hub-to-mounting-face

ET = hubFace − (width × 25.4 / 2)

The wheel's centerline sits at half its total width. Offset (ET) is the distance, in millimeters, between that centerline and the wheel's hub mounting face. Since measured overall wheel width is conventionally measured in inches, it's converted to millimeters (× 25.4) before halving. A positive ET means the mounting face sits toward the outside of centerline (wheel tucks in); a negative ET means it sits toward the inside (wheel pokes out). Width means measured overall flange width. Backspacing is rear flange edge to mounting pad. The nominal stamped bead-seat width must not be substituted.

Offset change → position shift and track width

shift = currentET − newET; trackWidthChange = shift × 2

When comparing a current offset to a new one, the position shift (per wheel) equals the current ET minus the new ET — a positive shift means the new wheel pokes further outward toward the fender. Because both wheels on an axle move the same amount, the total track width change is double the per-side shift. Width means measured overall flange width. Backspacing is rear flange edge to mounting pad. The nominal stamped bead-seat width must not be substituted.

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Glossary

Key Terms Explained

7 terms

Offset (ET) The distance, in millimeters, between a wheel's hub mounting face and its centerline. "ET" comes from the German "Einpresstiefe" (insertion depth), the industry-standard term stamped on most wheels.

Hub mounting face The flat surface on the back of the wheel that bolts flush against the vehicle's brake hub. This is the reference point offset is measured from.

Centerline The midpoint of the wheel's total width — halfway between the inner and outer lips of the barrel. Offset is measured relative to this line, not to either edge of the wheel.

Positive offset A hub mounting face positioned toward the outside (street side) of the wheel's centerline. Positive-offset wheels sit further inboard, tucked closer to the suspension — the norm on most modern factory wheels.

Negative offset A hub mounting face positioned toward the inside (brake side) of the wheel's centerline. Negative-offset wheels sit further outboard, closer to (or past) the fender — the classic "deep dish" look.

Backspacing A related measurement: the distance from the wheel's hub mounting face to its inner lip (rather than to the centerline). Backspacing and offset describe the same physical wheel from two different reference points, so they aren't interchangeable without knowing the wheel's total width.

Poke Slang for how far a wheel or tire extends outward past the fender's edge. Lower (or more negative) offsets increase poke; higher (or more positive) offsets reduce it.

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Scenarios

Real-World Examples

2 worked examples

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Measured overall width

Result

5.50 in backspacing

Overall flange width 9 in Offset +25.4 mm

An 8-inch nominal wheel may measure 9 inches overall, but the allowance must be verified; the equation uses the measured 9 inches.

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Inverse conversion

Result

+12.7 mm offset

Overall flange width 9 in Backspacing 127 mm (5 in)

Offset is 127 - 9 × 25.4 / 2 = 12.7 mm. No nominal-width or hidden flange assumption is used.

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Reference

Cite This Calculator

APA & MLA

Use either format to cite this calculator in a paper, report, or resource list.

APA

MLA

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Deep Dive

Understanding Wheel Offset (ET)

3 chapters · 4 min read

Wheel offset — often stamped as "ET" followed by a number — determines how far a wheel sits toward or away from the vehicle's suspension and fender. Getting it wrong can mean rubbing tires, uneven tire wear, or added stress on wheel bearings, so it's worth understanding before buying a new set of wheels or measuring a used one.

How offset is calculated

Offset uses the wheel centerline; backspacing uses the outer rear flange. Measure overall flange width for the centerline calculation. For an illustrative 8-inch nominal wheel measured 9 inches overall, +25.4 mm offset corresponds to 5.5 inches backspacing. At 127 mm backspacing and 9-inch overall width, offset is +12.7 mm. Actual flange projection must be measured or supplied by the manufacturer.

Why offset matters for fit

A wheel with too little offset (a very negative ET, or an ET much lower than stock) pushes the tire outward, increasing the chance it rubs the fender lip or fender liner, especially at full steering lock or over bumps. Too much offset (a high positive ET) pulls the wheel inward, which can cause the tire or wheel to contact suspension components, brake calipers, or the inner fender well. Manufacturers engineer a specific offset range for each vehicle to balance fender clearance, steering feel, and bearing load — deviating far from it (more than roughly ±10-15 mm on most cars, though this varies by vehicle) is where problems tend to start.

Offset vs. backspacing — don't confuse the two

Offset and backspacing both describe where a wheel's hub mounting face sits, but from different reference points: offset is measured from the wheel's centerline, while backspacing is measured from the wheel's inner lip. Two wheels with the same backspacing can have different offsets if their widths differ, and vice versa. When comparing wheels or planning a fitment change, make sure any spec sheet or forum post is describing offset (ET) and not backspacing before you use it in this calculator — mixing the two will produce a fender-fit estimate that's off by an amount depending on the wheel's width.

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Questions

Frequently Asked Questions

6 questions

What does a positive offset mean?+

A positive offset means the wheel's hub mounting face sits toward the outside (street side) of the wheel's centerline. This pulls the wheel's overall position inward, tucking it closer to the vehicle's suspension components — the standard setup on most modern factory wheels.

What does a negative offset mean?+

A negative offset means the wheel's hub mounting face sits toward the inside (brake side) of the wheel's centerline. This pushes the wheel further outward, toward or past the fender — the "deep dish" look common on trucks, muscle cars, and widened aftermarket setups.

Does a lower ET number always mean more poke?+

Relative to a given stock offset, yes — lowering the ET number (moving toward zero or negative) pushes the wheel further outward, increasing poke. Comparing two different offsets directly tells you the exact shift: use the Offset Change Effect tab to see how many millimeters a specific change moves the wheel.

Can the wrong offset cause fender rubbing?+

Yes. An offset that's too low (too negative, or well below the vehicle's stock spec) pushes the tire outward and increases the risk of rubbing the fender lip, especially during suspension travel or at full steering lock. Always check fender clearance — and consider a test-fit — before committing to a significant offset change.

Is offset the same as backspacing?+

Use measured overall flange width, not nominal stamped bead-seat width. Backspacing is the distance from the outer rear flange edge to the mounting pad. Confirm the manufacturer specification and actual fitment.

What units does this calculator use?+

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