Use our tire diameter calculator to calculate sidewall height, overall tire diameter, radius, circumference, and estimated revolutions per mile from a metric tire size.
Enter the tire width, aspect ratio, and wheel diameter shown on the tire sidewall. For example, a tire marked 225/60R17 is 225 mm wide, has a 60% aspect ratio, and fits a 17-inch wheel.
Enter Tire Size
Tire Dimensions
Calculation Summary
How to Use the Tire Diameter Calculator
Enter the three main parts of a metric tire size: width, aspect ratio, and wheel diameter. For a 225/60R17 tire, enter 225 for width, 60 for aspect ratio, and 17 for wheel diameter.
The calculator then estimates overall diameter, sidewall height, radius, circumference, and revolutions per mile and kilometer.
How Tire Diameter Is Calculated
Tire diameter is calculated from the tire width, aspect ratio, and wheel diameter.
First, sidewall height is calculated by multiplying tire width by the aspect ratio. Because a mounted tire has one sidewall above the wheel and another below it, two sidewalls are added to the wheel diameter.
For example, a 225/60R17 tire has a calculated sidewall height of 135 mm. Adding two 135 mm sidewalls to the 17-inch wheel produces an estimated diameter of approximately 27.63 inches.
What Does Tire Diameter Affect?
Overall tire diameter can affect several aspects of vehicle operation. Changing diameter may influence speedometer readings, effective gearing, ride height, wheel-well clearance, and the number of wheel revolutions required to travel a given distance.
A tire with a larger overall diameter travels farther during each revolution, while a smaller-diameter tire travels a shorter distance.
What Is Tire Sidewall Height?
Sidewall height is based on the tire’s aspect ratio. The aspect ratio is a percentage of the tire width rather than a fixed measurement.
For example, the sidewall of a 225/60 tire is approximately 60% of 225 mm, or 135 mm. A 225/45 tire has a shorter calculated sidewall because 45% of 225 mm is smaller.
Tire Circumference and Revolutions Per Mile
Circumference is the approximate distance around the tire. It determines how far the vehicle theoretically travels during one complete wheel revolution.
Revolutions per mile estimate how many rotations the tire makes while traveling one mile. Larger tires generally make fewer revolutions per mile than smaller tires.
Calculated Diameter vs. Actual Tire Diameter
The dimensions produced by this calculator are mathematical estimates based on the tire size marking. Actual mounted tire dimensions can differ slightly.
Differences can result from tire construction, tread design, manufacturer tolerances, wheel width, inflation pressure, load, and measurement methods. Manufacturer-published specifications should be used when exact dimensions are required.
Comparing Two Tire Sizes
If you want to compare two tire sizes rather than calculate one tire’s dimensions, use our Tire Size Comparison Calculator. It shows differences in diameter, width, sidewall height, circumference, ride height, revolutions per mile, and estimated speedometer readings.
Tire Diameter Calculator FAQ
What is the diameter of a 225/60R17 tire?
A 225/60R17 tire has a calculated overall diameter of approximately 27.63 inches, although actual manufacturer specifications may vary slightly.
Does a larger tire diameter raise the vehicle?
Increasing overall tire diameter can increase vehicle ride height by approximately half of the diameter increase, assuming all other factors remain unchanged.
Does tire width determine tire diameter?
Tire width contributes to diameter because sidewall height is calculated as a percentage of width. Width alone does not determine diameter; aspect ratio and wheel diameter are also required.
Why does actual tire diameter differ from calculated diameter?
Tire size markings describe nominal dimensions. Actual measurements can vary by manufacturer, tread design, tire construction, wheel width, inflation pressure, and load.
Can tire diameter affect the speedometer?
Yes. Changing rolling diameter changes the distance traveled during each tire revolution and can therefore affect the relationship between indicated and actual vehicle speed.
Explore More Tire and Wheel Tools
Learn more about tire sizes, compare two sizes with our Tire Size Comparison Calculator, or browse our Tire and Wheel Calculators & Fitment Tools.
Calculated Dimensions Do Not Confirm Fitment
Tire diameter is only one part of vehicle fitment. Before changing tire size, verify tire width, load rating, speed rating, wheel compatibility, brake and suspension clearance, fender clearance, inflation requirements, and specifications for your exact vehicle.