Rim Diameter Calculator
Find the rim size from the tire's height and sidewall. Use the calculator below. Results update as you type.
Overall Diameter = (Rim Diameter × 25.4) + 2 × (Width × Aspect Ratio / 100)How the Rim Diameter Calculator Works
This calculator works by subtracting two sidewall heights from the overall diameter. It solves the wheel size that fits a known tire height and profile.
- Enter the target overall diameter, for example 28.5 in (723.9 mm).
- Enter the section width and aspect ratio, for example 235 and 60.
- Read the rim diameter: 17.4 in, which rounds to a 17 in wheel.
- Check the reverse result by entering 235/60R17 in the diameter tool: 28.10 in.
The tool works in both directions: from a full size code it confirms the rim, and from a height target it solves the rim.
The Formula
The formula is Rim Diameter = (Overall Diameter − 2 × Sidewall Height) ÷ 25.4, with diameter and sidewall in millimeters.
Rim Diameter (in) = (Overall Diameter (mm) − 2 × Width × Aspect Ratio ÷ 100) ÷ 25.4 Overall Diameter (mm) = (Rim Diameter × 25.4) + 2 × (Width × Aspect Ratio ÷ 100)Worked example: a 31.6 in (802.6 mm) tire with a 265/70 cross-section has 2 × 185.5 = 371 mm of sidewall. 802.6 − 371 = 431.6 mm, and 431.6 ÷ 25.4 = 16.99 in, so the wheel is 17 in.
Passenger and truck rims come in whole inches from 13 in to 26 in. Commercial trucks use half-inch sizes: 17.5, 19.5, 22.5 and 24.5 in.
Conversion Table
The conversion table converts 12 rim sizes from inches to millimeters and centimeters and shows one example tire for each rim. The last column solves the rim back from that tire, proving the formula.
A 17 in rim is 431.8 mm (43.18 cm). The 225/45R17 example solves back to exactly 17.0 in, confirming the size code.
| Rim (in) | Rim (mm) | Rim (cm) | Example size on this rim | Solved rim from that size (in) |
|---|---|---|---|---|
| 13 | 330.2 | 33.02 | 155/80R13 | 13.0 |
| 14 | 355.6 | 35.56 | 175/70R14 | 14.0 |
| 15 | 381.0 | 38.10 | 195/65R15 | 15.0 |
| 16 | 406.4 | 40.64 | 205/55R16 | 16.0 |
| 17 | 431.8 | 43.18 | 225/45R17 | 17.0 |
| 18 | 457.2 | 45.72 | 235/40R18 | 18.0 |
| 19 | 482.6 | 48.26 | 245/35R19 | 19.0 |
| 20 | 508.0 | 50.80 | 255/35R20 | 20.0 |
| 21 | 533.4 | 53.34 | 265/35R21 | 21.0 |
| 22 | 558.8 | 55.88 | 285/45R22 | 22.0 |
| 24 | 609.6 | 60.96 | 305/35R24 | 24.0 |
| 26 | 660.4 | 66.04 | 305/30R26 | 26.0 |
What Is the Rim Diameter Calculator?
The Rim Diameter Calculator is a tool that finds the wheel diameter, in inches and millimeters, from a tire's overall height and sidewall dimensions. Rim diameter is the bead seat diameter: the diameter where the tire bead locks onto the wheel.
The rim number in a size code must match the wheel exactly. A 17 in tire does not fit a 17.5 in or 16 in rim. The bead seat diameter is a fixed standard, which makes it the one tire dimension with zero tolerance.
Common Uses
This calculator has 4 uses: plus-size planning, mystery-wheel checks, height-target solving and code verification.
- Plan plus sizes: Find which wheel diameter keeps a target tire height.
- Check unknown wheels: Convert a measured bead seat diameter to the nominal inch size.
- Solve height targets: Pick the rim that fits a 33 in or 35 in (838 or 889 mm) tire with a set profile.
- Verify size codes: Confirm that a listed diameter matches the stated rim.