Back to Home

Tire Size Calculator

Enter a metric tire size (e.g. 225/45R17) to calculate overall diameter, sidewall height, circumference, and revolutions per mile. Enable comparison mode to see two sizes side by side.

Tire 1

MeasurementValue

About This Calculator

Tire sizes are expressed in a metric format like 225/45R17, where 225 is the tread width in millimeters, 45 is the sidewall height as a percentage of the width (the aspect ratio), and R17 means it fits a 17-inch rim. This calculator converts those numbers into the overall tire diameter, sidewall height, rolling circumference, and revolutions per mile. When shopping for replacement tires or considering a size change, comparing these dimensions tells you how much your speedometer reading, ground clearance, and ride height will change.

FAQ

What does the tire size 225/45R17 mean?
225 is the tread width in mm. 45 is the aspect ratio, meaning the sidewall height is 45% of the width (101.25 mm). R means radial construction, and 17 is the rim diameter in inches.
How much diameter change is acceptable?
Most manufacturers recommend staying within 3% of the original tire diameter to avoid speedometer errors, ABS issues, and clearance problems. This calculator shows the exact percentage difference when comparing two sizes.
How does tire size affect speedometer accuracy?
A larger tire covers more ground per revolution, so your speedometer will read lower than actual speed (you are going faster). A smaller tire does the opposite. A 3% diameter increase means roughly 3% speedometer error.
What are revolutions per mile used for?
Revolutions per mile indicates how many times the tire rotates over one mile. It is used to calibrate speedometers, calculate gear ratios, and compare tire sizes. Fewer revs per mile means a larger tire diameter.

Related Tools

Fuel Cost Engine Displacement Speed