Wheel Circumference Calculator

Setting Up Your Bike Computer

To get accurate speed and distance data on non-GPS bike computers (or when using a speed sensor indoors), you must manually input the Wheel Circumference.

Most manuals provide a generic chart, but calculating it based on your specific tire width (ISO/ETRTO) is more accurate.

What is ISO / ETRTO?

The ETRTO (European Tyre and Rim Technical Organisation) standard is the universal language of tires. It avoids the confusion of "29 inch" vs "700c" (which are actually the same rim diameter).

• The First Number (e.g., 25): The inflated width of the tire in millimeters.
• The Second Number (e.g., 622): The bead seat diameter (BSD) of the rim in millimeters.

The "Rollout" Method (100% Accuracy)

While this calculator provides a mathematical ideal, tire pressure and rider weight can compress the tire, slightly reducing the effective circumference. For maximum precision:

1. Find a valve stem on your front wheel and place it at the absolute bottom (6 o'clock).
2. Mark the floor with chalk or tape exactly aligned with the valve.
3. Sit on the bike (to account for weight squash) and roll forward one full revolution until the valve is at the bottom again.
4. Mark the new spot and measure the distance between marks in millimeters.

Common Circumference Reference Chart

Knowing your exact wheel circumference helps if you want to calculate Speed from Cadence or Gear Inches with precision.