Tire Size Converter
Decode metric tire sizes like 225/45R17 and calculate overall diameter, circumference, and sidewall height.
Enter a metric tire size to see its actual dimensions in both metric and imperial.
A tire size like 225/45R17 means:
- 225 = tread width in millimeters
- 45 = aspect ratio (sidewall height as % of width)
- R = radial construction
- 17 = wheel (rim) diameter in inches
Calculating overall tire diameter:
- Sidewall height = width × (aspect ratio / 100)
- Sidewall height in inches = sidewall height (mm) ÷ 25.4
- Overall diameter = (2 × sidewall in inches) + rim diameter
Example for 225/45R17:
- Sidewall = 225 × 0.45 = 101.25 mm = 3.986 inches
- Overall diameter = (2 × 3.986) + 17 = 24.97 inches (634 mm)
- Circumference = diameter × π = 78.44 inches (1,992 mm)
Revolutions per mile:
- Revs/mile = 63,360 ÷ circumference (inches)
- Revs/km = 1,000,000 ÷ circumference (mm)
Common tire sizes:
| Size | Diameter (in) | Diameter (mm) | Circ (in) |
|---|---|---|---|
| 205/55R16 | 24.9 | 632 | 78.2 |
| 225/45R17 | 25.0 | 634 | 78.4 |
| 235/40R18 | 25.4 | 645 | 79.8 |
| 245/45R19 | 27.7 | 703 | 86.9 |
| 265/70R17 | 31.6 | 803 | 99.4 |