Wheel Offset Calculator
Calculate wheel offset (ET) from backspacing and wheel width. Positive, zero and negative offset explained with mm and inch results.
Calculate wheel mounting offset.
Wheel Offset Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Wheel Offset Calculator Works?
The Wheel Offset Calculator works by subtracting half of the wheel's overall width from its backspacing. The tool uses 3 steps.
Enter wheel width
Type the nominal width, for example 8.5 in. The calculator adds 1 in for the 2 flanges to get a 9.5 in (241.3 mm) overall width.
Enter backspacing
Measure from the hub mounting face to the inner flange edge, for example 6.5 in (165.1 mm).
Read the offset
The calculator subtracts half the overall width (120.65 mm) from 165.1 mm and returns ET+44.
Wheel Offset Calculator Formula
The Wheel Offset Calculator formula is ET = Backspacing − (Wheel width + 1 in) ÷ 2, with all values in millimeters.
W_o = (W_nom + 1) × 25.4CL = W_o ÷ 2ET = BS − CL- W_nom
- Nominal wheel width (in)
- BS
- Backspacing (mm)
- ET
- Offset from centerline to mounting face (mm)
Worked example
A 9.0 in wheel with 5.0 in (127 mm) of backspacing has a centerline at 127 mm. The offset is 127 − 127 = ET 0. With 4.5 in (114.3 mm) of backspacing, the offset is ET −13.
Wheel Offset Calculator Conversion Table
The Wheel Offset Calculator conversion table converts 7 width and backspacing pairs into offset (ET).
| Wheel width | Backspacing | Half overall width | Offset |
|---|---|---|---|
| 7.0" (178 mm) | 5.5 in (139.7 mm) | 101.6 mm | ET+38 |
| 7.5" (190 mm) | 6.0 in (152.4 mm) | 107.9 mm | ET+44 |
| 8.0" (203 mm) | 6.0 in (152.4 mm) | 114.3 mm | ET+38 |
| 8.5" (216 mm) | 6.5 in (165.1 mm) | 120.6 mm | ET+44 |
| 9.0" (229 mm) | 5.0 in (127.0 mm) | 127.0 mm | ET+0 |
| 9.0" (229 mm) | 4.5 in (114.3 mm) | 127.0 mm | ET-13 |
| 10.0" (254 mm) | 5.0 in (127.0 mm) | 139.7 mm | ET-13 |
What is Wheel Offset Calculator?
A Wheel Offset Calculator is a tool that finds the distance between a wheel's mounting face and its centerline. Offset, marked ET from the German Einpresstiefe, is stamped on most wheels in millimeters.
Positive offset puts the mounting face outboard of the centerline and tucks the wheel in. Negative offset pushes the wheel out from the hub. Most front-drive cars use ET35 to ET50, and many trucks use ET−12 to ET+25.
The calculator uses the industry convention of adding 1 in to the nominal width for the flanges.
What are the uses of Wheel Offset Calculator?
There are 4 main uses of the Wheel Offset Calculator, including unmarked wheel identification and used wheel checks.
Unmarked wheels
Find the offset of a wheel with no ET stamp.
Used wheel checks
Confirm a seller's offset claim with a tape measure.
Fitment planning
Convert truck-style backspacing into the ET most catalogs list.
Custom wheel orders
Specify offset for a made-to-order wheel.
Related Wheel Geometry & Fitment Tools
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