Inch-to-Metric Tire Converter
Find the metric size that is close to an inch size. Use the calculator below. Results update as you type.
How the Inch-to-Metric Tire Converter Works
The Inch to Metric Tire Converter works by searching metric sizes on the same rim and ranking them by how closely their diameter and width match the inch size. It returns the closest metric match and the gap in percent.
- Enter the inch size, for example 33x12.50R15.
- Let the tool test metric widths and aspect ratios on a 15 in rim.
- Read the closest metric size: 325/70R15 at 32.91 in.
- Check the gap: −0.26% in diameter.
The tool weighs diameter more than width. A close diameter keeps speedometer and gearing changes small.
The Formula
The Inch to Metric Tire Converter formula finds the aspect ratio that gives the target height on the chosen width and rim.
Aspect Ratio = ((Diameter (in) − Rim) ÷ 2 × 25.4) ÷ Width (mm) × 100 Width (mm) = Width (in) × 25.4Worked example for 35x12.50R17: the width is 12.5 × 25.4 = 317.5 mm, so the nearest widths are 315 and 325. On a 325 mm width, the aspect ratio is (9.0 × 25.4) ÷ 325 × 100 = 70.3%, which rounds to 70. The match is 325/70R17 at 34.91 in.
Conversion Table
The Inch to Metric Tire Converter conversion table gives the closest metric size for 8 flotation sizes. Every match sits within ±0.53% of the inch size's diameter.
Some matches are uncommon sizes. A 255/80R17 matches a 33x10.50R17 within 0.19%, but few tire models come in that size. Check availability before you commit to a match.
| Inch Size | Closest Metric Size | Metric Diameter (in) | Diameter Difference | Metric Width (in) |
|---|---|---|---|---|
| 31x10.50R15 | 255/80R15 | 31.06 | +0.20% | 10.04 |
| 33x12.50R15 | 325/70R15 | 32.91 | -0.26% | 12.80 |
| 33x10.50R17 | 255/80R17 | 33.06 | +0.19% | 10.04 |
| 35x12.50R17 | 325/70R17 | 34.91 | -0.25% | 12.80 |
| 35x12.50R20 | 315/60R20 | 34.88 | -0.34% | 12.40 |
| 37x12.50R17 | 315/80R17 | 36.84 | -0.43% | 12.40 |
| 37x13.50R20 | 335/65R20 | 37.15 | +0.39% | 13.19 |
| 32x11.50R15 | 285/75R15 | 31.83 | -0.53% | 11.22 |
What Is the Inch-to-Metric Tire Converter?
The Inch to Metric Tire Converter is a tool that finds metric tire sizes close to an inch-based flotation size. It helps when a tire you want comes only in metric sizes, or when a vehicle placard lists a flotation size.
The converter returns approximate equivalents. Flotation and metric tires built to the same nominal height still differ by 0.2–0.5 in (5–13 mm) in measured diameter across brands.
Common Uses
The Inch to Metric Tire Converter has 4 uses: finding alternatives, widening model choice, matching AWD sets and pricing comparisons.
- Find alternatives: Locate metric sizes near a flotation size.
- Widen model choice: Access tire models sold only in metric sizes.
- Match AWD sets: Pick a metric size close to the existing flotation tires.
- Compare prices: Price the same height across both size systems.