Tire Size Calculator
Turn a tire code like 225/45R17 into real measurements — overall diameter, sidewall height, circumference, and revolutions per mile.
Enter a tire code like 225/45R17.
Decoding tire size codes
A tire size like 225/45R17 packs three measurements into one code. The first number (225) is the section width in millimeters. The second (45) is the aspect ratio — the sidewall height as a percentage of the width. The "R" means radial construction, and the last number (17) is the wheel diameter in inches.
This calculator converts that code into the overall tire diameter, sidewall height, circumference, and revolutions per mile. That matters because changing tire size affects your speedometer accuracy, ride height, and clearance.
Frequently asked questions
What does 225/45R17 mean?
225 mm wide, sidewall 45% of width, radial, on a 17-inch wheel. This tool turns those into real diameter and circumference figures.
Will a different size break my speedometer?
A larger or smaller overall diameter makes the speedometer read low or high. Keep within ~3% of stock to stay accurate.
Can I put wider tires on my car?
Often, within limits set by your wheels and fenders. Check fitment, keep diameter close to stock, and verify proper load ratings.