How to use it
- Type the Rim width in millimetres, from the wheel's specification.
- Enter the Backspacing: the distance from the hub face to the inner edge of the rim, in millimetres.
- Read Wheel offset (ET). A plus sign means the hub face is on the outer side of the centre line, a minus sign on the inner side.
- Check Hub face to outer rim edge and Hub face to centre line for the distances on each side.
How the offset is defined
The EU definition of wheel offset is the distance from the hub abutment face to the centre line of the rim (Commission Regulation (EU) No 458/2011, Article 2(4)). The hub abutment face is the flat face where the wheel sits against the hub.
The offset has a sign. Measured from the inner edge, the hub face sits at the backspacing, and the centre line sits at half the rim width. So the offset is the backspacing minus half the rim width.
Offset (mm) = backspacing (mm) − rim width (mm) ÷ 2
Hub face to outer rim edge (mm) = rim width (mm) − backspacing (mm)
Hub face to centre line (mm) = size of the offsetReading the sign
- A plus sign means the hub face is on the outer side of the centre line, so the hub face is nearer the outer edge of the rim.
- A minus sign means the hub face is on the inner side of the centre line, so more of the rim sits outboard of the hub.
- The regulation gives the distance without a sign. The sign is the convention this calculator uses.
What this calculator does not include
- Whether a wheel fits a car. The bolt pattern, the centre bore, the load rating and the permitted sizes come from the vehicle documents or the maker.
- Clearance to the body, the brakes and the suspension. These need a check on the car itself.
- A measured value can differ from the figure the maker gives, so check the figure you measured before you buy.
Worked example: 200 mm rim, backspacing 112 mm
The centre line is 200 ÷ 2 = 100 mm from the inner edge, and the hub face is 112 mm from the inner edge. The offset is 112 − 100 = +12 mm: the hub face is on the outer side of the centre line.
The hub face is 200 − 112 = 88 mm from the outer edge and 12 mm from the centre line.
| Measure | Value (mm) |
|---|---|
| Wheel offset (ET), with its sign | 12.0 |
| Hub face to outer rim edge | 88.0 |
| Hub face to centre line | 12.0 |
Frequently asked questions
What is wheel offset?
It is the distance from the hub abutment face, where the wheel sits against the hub, to the centre line of the rim, in millimetres. The EU regulation defines it this way.
What does a positive offset mean?
A plus value means the hub face is on the outer side of the centre line, so the hub face is nearer the outer edge of the rim. This sign is the convention of this calculator; the regulation gives the distance without a sign.
What is backspacing?
It is the distance from the hub face to the inner edge of the rim. With the rim width it gives the offset: the backspacing minus half the rim width.
Why does the offset matter when I change wheels?
The offset sets how far the wheel sits in or out relative to the hub. A different offset moves the wheel in or out, so compare the figure with the vehicle documents or the maker's list.
Does the calculator check whether a wheel fits my car?
No. It calculates the offset from the two measurements. Whether a wheel fits depends on the vehicle, its bolt pattern, its load rating and its permitted sizes, so check those in the vehicle documents or the maker's list.
Does the calculator keep the numbers I type?
The page works in your browser and sends nothing to a server. The numbers stay in the page address, so a copied link shows the same figures.
Sources
Figures and text last checked on Thursday, November 12, 2026.