Wheel Width Calculator
Compare rim widths for a tire. Use the calculator below. Results update as you type.
How the Wheel Width Calculator Works
This calculator works by converting rim width between inches and millimeters and showing the half-width used in offset math. Wheel width is measured between the bead seats, not across the outer flanges.
- Enter the rim width, for example 8.5 in.
- Read the width in millimeters: 215.9 mm.
- Read the half-width: 108.0 mm.
- Read the approximate overall width including flanges: 241.3 mm.
The Formula
The formula is Width (mm) = Width (in) × 25.4. Half-width is width divided by 2.
Width (mm) = Width (in) × 25.4 Half Width (mm) = Width (mm) ÷ 2 Overall Width ≈ (Width (in) + 1) × 25.4Worked example: a 9.5 in wheel is 241.3 mm wide between bead seats, has a 120.7 mm half-width and measures about 266.7 mm across the flanges.
Conversion Table
The conversion table converts 13 rim widths from 5.5 in to 12.0 in into millimeters, half-widths and approximate overall widths. Each 0.5 in step adds 12.7 mm.
The half-width column feeds directly into backspacing, frontspacing and inner and outer position formulas.
| Rim Width (in) | Rim Width (mm) | Half Width (mm) | Overall Width incl. Flanges (mm, approx.) |
|---|---|---|---|
| 5.5 | 139.7 | 69.8 | 165.1 |
| 6.0 | 152.4 | 76.2 | 177.8 |
| 6.5 | 165.1 | 82.5 | 190.5 |
| 7.0 | 177.8 | 88.9 | 203.2 |
| 7.5 | 190.5 | 95.2 | 215.9 |
| 8.0 | 203.2 | 101.6 | 228.6 |
| 8.5 | 215.9 | 107.9 | 241.3 |
| 9.0 | 228.6 | 114.3 | 254.0 |
| 9.5 | 241.3 | 120.6 | 266.7 |
| 10.0 | 254.0 | 127.0 | 279.4 |
| 10.5 | 266.7 | 133.3 | 292.1 |
| 11.0 | 279.4 | 139.7 | 304.8 |
| 12.0 | 304.8 | 152.4 | 330.2 |
Wheel width is measured between the bead seats; the flanges add about 1 in (25 mm) to the outside width.
What Is the Wheel Width Calculator?
The Wheel Width Calculator is a tool that converts and compares rim widths for tire fitment and offset math. Rim width is the second number in a wheel marking such as 17x8.0 ET40.
Rim width decides which tire widths mount safely and how far the wheel extends in each direction from its center plane.
Common Uses
This calculator has 4 uses: tire matching, offset math, wheel comparison and catalog reading.
- Match tires: Compare rim width with the tire's approved range.
- Run offset math: Use the half-width in position formulas.
- Compare wheels: See how much wider a new wheel is.
- Read catalogs: Convert widths listed in mm or inches.