# Wheel Offset Calculator

URL: https://speedycalculator.com/calculators/everyday-life/wheel-offset/
Last updated: 2026-10-25

> The wheel offset calculator shows how a new wheel's width and offset change its position – how much closer it moves to the suspension and how much further it sticks out towards the fender – compared with your current wheels.

## Inputs

- Current wheel width (in, mm)
- Current offset (ET) (mm, in)
- New wheel width (in, mm)
- New offset (ET) (mm, in)

## Results

- Inner edge moves towards suspension by
- Outer edge moves out towards fender by
- New backspacing (inner edge to mounting face)

## Formula

```
Inner edge from hub face = width ÷ 2 + offset
Outer edge from hub face = width ÷ 2 − offset
Change = new − current (positive inner = closer to the strut; positive outer = further out)
```

## Explanation

Offset is the distance from the wheel's centreline to its mounting face, in millimetres. Higher positive offset pulls the wheel inwards; lower or negative offset pushes it out. When you change wheel width or offset, check both the inner clearance to the suspension and the outer clearance to the fender lip.

### How to use the Wheel Offset Calculator

- **Current wheel width**
- **Current offset (ET)**
- **New wheel width**
- **New offset (ET)**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the width and offset of your current and new wheels.

### Tips

- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field's menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.

### Common mistakes to avoid

- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.

### Inputs explained

FieldWhat to enterCurrent wheel widthUnits: in, mmCurrent offset (ET)Units: mm, inNew wheel widthUnits: in, mmNew offset (ET)Units: mm, in

### What each result means

- **Inner edge moves towards suspension by** = ([New wheel width]÷2 + [New offset (ET)]) - ([Current wheel width]÷2 + [Current offset (ET)])
- **Outer edge moves out towards fender by** = ([New wheel width]÷2 - [New offset (ET)]) - ([Current wheel width]÷2 - [Current offset (ET)])
- **New backspacing (inner edge to mounting face)** = [New wheel width]÷2 + [New offset (ET)] + 0.0127

### Example values

How the main result changes when **Current wheel width** changes and everything else stays at the example values above:

Current wheel width (in)Inner edge moves towards suspension by (mm)3.7550.35.6326.57.52.79.38-21.111.25-44.915-92.6

## Worked example

Inputs — Current wheel width: 7.5 in; Current offset (ET): 45 mm; New wheel width: 8.5 in; New offset (ET): 35 mm.

Results — **Inner edge moves towards suspension by = 2.7 mm**; Outer edge moves out towards fender by = 22.7 mm; New backspacing (inner edge to mounting face) = 6.13 in.

## FAQ

**What is wheel offset (ET)?**
The distance in mm from the wheel's centreline to the mounting face. Positive offset puts the face towards the outside of the wheel.

**Will a lower offset stick out more?**
Yes – each 1 mm lower offset moves the wheel 1 mm outwards.

**What is backspacing?**
The distance from the mounting face to the inner rim edge, usually in inches; it is width ÷ 2 + offset plus the rim lip (about ½ in).

**What formula does the Wheel Offset Calculator use?**
Inner edge from hub face = width ÷ 2 + offset.