Tire Size Calculator

For an automobile tire, multiply section width by the aspect ratio percentage to get sidewall height, then add two sidewalls to the rim diameter. For bicycle sizes such as 700x25c, the calculator uses the bead-seat diameter plus two section widths.

When the new tire has a larger circumference, a speedometer calibrated for the original tire reads lower than your actual speed. This calculator shows both the actual speed when the speedometer reads 100 and the displayed speed at an actual 100.

No. It calculates nominal dimensions and differences only. Fitment depends on your vehicle, wheel width, suspension, load rating, speed rating, and installed clearance, so confirm any tire change with a qualified tire professional.

Automobile sizes can use formats such as 205/55R16, 205 55 16, or 205-55-16. Bicycle sizes support French sizes such as 700x25c and common mountain formats such as 29x2.25.