Free wheel and tyre tools
Metric and inch tyre size converter
Convert metric tyre sizes to diameter and width in inches. Convert flotation-style inch dimensions to an unrounded metric width and profile.
How it works
One inch is exactly 25.4 mm. A metric tyre's diameter is the rim diameter plus twice its sidewall height. Inch or flotation-style notation puts overall diameter first, then section width, then rim diameter. For the reverse conversion, profile = (overall diameter − rim diameter) ÷ (2 × section width) × 100, with all three dimensions in inches. We keep the result unrounded to standard tyre increments so it is not mistaken for a size sold by a manufacturer.
References
A worked example
265/70 R17 converts to a nominal 31.61 inch diameter and 10.43 inch width on a 17 inch rim. In the other direction, 33 × 12.5 R17 gives 317.5 mm width and a 64% profile. Those are dimensional equivalents, not an instruction to order a 317.5/64 R17 tyre.
Quick reference
Inch tyre sizes in metric
| Inch size | Width | Profile | Rim |
|---|---|---|---|
| 31x10.50R15 | 266.7 mm | 76.2% | 15 inch |
| 33x12.50R15 | 317.5 mm | 72% | 15 inch |
| 33x12.50R17 | 317.5 mm | 64% | 17 inch |
| 35x12.50R17 | 317.5 mm | 72% | 17 inch |
| 35x12.50R20 | 317.5 mm | 60% | 20 inch |
| 37x12.50R17 | 317.5 mm | 80% | 17 inch |
Metric truck sizes in inches
| Metric size | Diameter | Width |
|---|---|---|
| 265/70 R17 | 31.61 in | 10.43 in |
| 285/70 R17 | 32.71 in | 11.22 in |
| 275/65 R18 | 32.07 in | 10.83 in |
| 285/75 R16 | 32.83 in | 11.22 in |
| 315/70 R17 | 34.36 in | 12.4 in |
Nominal dimensions. Real tyres vary by model, so a 285/70 R17 is often sold as a 33.
Explained in our guides
- Lifted truck wheel fitment: backspacing, 33s, 35s and trimmingPlan larger truck tyres around lift-kit requirements, backspacing, steering and articulation. Compare 33 and 35 inch tyres without assuming a lift guarantees clearance.
- How to read a tyre size, load index and sidewall markingsDecode tyre width, aspect ratio, rim diameter, load and speed markings, then calculate sidewall height and diameter using a 225/45 R17 example.
Questions
Is a 33 inch tyre exactly 33 inches tall?
Not necessarily. Inch designations are nominal too. Actual dimensions and rolling circumference vary by tyre model, rim, load, pressure and wear. Use the specific manufacturer's dimensions for clearance planning.
Can I round the result to the nearest available tyre?
Rounding width and profile changes diameter. Use the plus-size or tyre comparison calculator to check a real, available candidate, then verify rim approval, load and speed ratings and vehicle clearances.
Does this change the load rating or construction?
No. It only converts nominal geometry. LT, P-metric and other constructions can have different load and pressure requirements, even when their outer dimensions are similar.
Keep checking
Use these results to plan a setup. Confirm fitment, tyre approval and clearances with a qualified professional before buying or fitting parts.