Tire Size Calculator
Enter your tire's width, aspect ratio, and rim diameter to decode the full size — diameter, sidewall height, circumference, and revolutions per mile.
How It Works
A tire size like 225/45R17 contains three key numbers:
- 225 — Section width in millimeters
- 45 — Aspect ratio: sidewall height as a percentage of width
- 17 — Rim (wheel) diameter in inches
Formula
Diameter = (2 × width × aspectRatio / 2540) + rimDiameter
The constant 2540 converts millimeters to inches (25.4 mm/in × 100 for the percentage).
Frequently Asked Questions
How do I read a tire size like 225/45R17?
225 is the section width in mm, 45 is the aspect ratio (sidewall height as % of width), R means radial construction, and 17 is the rim diameter in inches.
How is overall tire diameter calculated?
Overall diameter = (2 × width × aspectRatio / 2540) + rimDiameter. The formula converts the sidewall height from mm to inches and adds it twice (top and bottom) to the rim diameter.