Wheel Offset Calculator

Written byOleh Soloninupdated 25 September 2026

Original rim width, inches

Original offset ET, mm

New rim width, inches

New offset ET, mm

Result

Verdict
The wheel grows both ways: check the arch lip and the clearance to the strut
Shift outward, mm17.7
Shift inward, mm7.7
ET for the same outer position57.7
Spacer required
will not help: the wheel already sits 17.7 mm further out, and a spacer pushes it further still
Change in ET, mm-5

Width and offset work together

Shows how far a new wheel moves outward towards the arch and inward towards the strut compared with the original, and what spacer would cancel the difference.

Offset, or ET, is the distance in millimetres from the wheel's mounting face to its centreline. The higher the ET, the deeper the wheel sits in the arch. On its own the number says little: where the wheel ends up depends on offset and width together.

The outer edge of the rim sits half the width minus the offset from the hub face; the inner edge sits half the width plus the offset. That is why a wider wheel with a lower ET pushes out twice over — once for the width and once for the offset.

How to use

Enter the original rim width in inches and its offset, as stamped on the wheel — for example 6.5J ET45.
Enter the width and offset of the new wheel.
Read how far the outer and inner edges move, and which offset would keep the outer edge where it was.

How width and offset move the wheel

Each row is a separate run of the calculator from the original wheel. A plus means the edge moved away from the wheel's centre, outwards or inwards; a minus means it moved back.

Every row comes from the calculator on this page.
From	To	Outer edge	Inner edge	ET to keep the outer edge
6.5J ET45	7J ET45	+6.3 mm	+6.3 mm	51.4
6.5J ET45	7J ET38	+13.3 mm	−0.7 mm	51.4
6.5J ET45	7.5J ET40	+17.7 mm	+7.7 mm	57.7
6.5J ET45	8J ET35	+29.1 mm	+9 mm	64.1
7J ET35	7J ET45	−10 mm	+10 mm	35

What this calculator shows

How far the outer edge moves — towards the arch lip
How far the inner edge moves — towards the strut and caliper
The offset that would put the new wheel's outer edge where the old one was

What to keep in mind

The calculation is geometric: it knows nothing about spoke shape, caliper size or the arches of a particular car.
The 5 mm in the verdict is the calculator's cue to check clearances, not a rule.

FAQs

What is wheel offset in plain terms?

The distance in millimetres from the face that bolts to the hub to the middle of the rim. A positive offset means the mounting face is outboard of the centreline, so the wheel sits deeper in the arch.

Does a lower ET always stick out more?

At the same width, yes. Dropping ET by 10 mm moves the wheel exactly 10 mm outward and takes the same 10 mm away from the strut.

Can spacers fix the offset?

A spacer moves the wheel outward by exactly its own thickness. Nothing moves a wheel inward, so a rim with too little offset cannot be corrected with one.

How do I convert rim width from inches?

Multiply by 25.4: 6.5J is 165.1 mm and 7.5J is 190.5 mm. An extra inch of width splits evenly — 12.7 mm out and 12.7 mm in — if the offset stays the same.

What offset keeps a wider wheel flush?

The original plus 12.7 mm for every inch of extra width. From 6.5J ET45, a 7.5J needs ET 57.7 and an 8J needs ET 64.1; then all the extra width goes inward.

What should I check after fitting new wheels?

Clearance from the tyre to the arch lip with the suspension compressed, and to the strut and caliper at full lock. The calculator tells you how far the edges moved; whether there is room only shows on the car.

Worked example

From 6.5J ET45 to 7.5J ET40

Input: 6.5J ET45 → 7.5J ET40

Output: 17.7 mm further out, 7.7 mm further in

Note: An inch of width is 25.4 mm, 12.7 each side, and the lower offset adds another 5 mm on the outside. To keep the outer edge in place the new wheel would need ET 57.7.

Useful links

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Wheel Offset Calculator

Result

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