Wheel Circumference Calculator

Your bike computer calculates speed and distance by counting wheel rotations and multiplying by the wheel circumference. If the circumference value is wrong, every speed reading and distance measurement will be off. A 2% error in circumference means a 2% error in reported distance - that 100 km ride was actually 98 km or 102 km.

Tire size has a significant impact on circumference. Using the standard π × diameter model, a 700×23c wheel is about 2096mm, 700×25c is about 2105mm, and a 26×2.1 wheel is about 2070mm. Switching from a 700×25c to a 700×32c tire adds about 50mm to the circumference. Even changing brands with the same stated size can vary by 5–10mm due to manufacturing differences. For the best accuracy, calibrate whenever you change tires.

1. Calculator method:Use this tool to find the circumference for your tire size, then enter it in your device's settings (look for "wheel size" or "wheel circumference").
2. Manual roll-out method: Mark the ground at the tire valve, sit on the bike, roll forward exactly one wheel revolution until the valve returns to the bottom, and measure the distance. This accounts for tire deflection under your weight.