Calculate tire dimensions, compare sizes, and find speedometer differences
Our Tire Size Calculator computes key tire dimensions from a standard tire size code (e.g., P225/65R17) or manual entry. It calculates section width, sidewall height, tire diameter, circumference, and revolutions per mile. The compare feature lets you evaluate plus sizing by comparing two tire sizes side by side, including the speedometer difference.
Understanding tire dimensions is essential for selecting replacement tires, upgrading wheels, or ensuring proper fitment on your vehicle.
P = Passenger tire, 225 = section width in millimeters, 65 = aspect ratio (sidewall height is 65% of width), R = radial construction, 17 = wheel diameter in inches.
A larger tire diameter reduces the displayed speed relative to actual speed (speedometer reads slower). A smaller diameter increases the displayed speed. Use the comparison feature to see the exact percentage difference between two tire sizes.