Bicycle Computer Circumference Calculator
Set your bike computer with the right wheel size. Use the calculator below. Results update as you type.
Circumference = π × Overall DiameterHow the Bicycle Computer Circumference Calculator Works
This calculator works by computing π × (BSD + 2 × width), or by dividing a measured rollout by the number of turns. Bike computers ask for the wheel circumference in mm.
- Enter the ETRTO size, for example 28-622.
- Read the calculated circumference: 2,130 mm (83.9 in).
- For best accuracy, roll the bike with the rider seated for 1 turn and measure the distance.
- Enter the measured rollout in the computer.
The Formula
The formula is Circumference = π × (BSD + 2 × Width).
Circumference = π × Overall Diameter Overall Diameter ≈ BSD + 2 × Width Measured Rollout = Distance ÷ TurnsWorked example: 56-622 (29 x 2.2) gives π × (622 + 112) = 2,306 mm (90.8 in).
Conversion Table
The conversion table lists calculated circumference for 11 bicycle tire sizes. Values run from 1,571 mm (20 x 1.75) to 2,337 mm (29 x 2.4).
The note under the table explains why calculated values run slightly above measured rollouts.
| Tire | ETRTO | Circumference (mm) | Circumference (in) |
|---|---|---|---|
| 700x23c | 23-622 | 2,099 | 82.6 |
| 700x25c | 25-622 | 2,111 | 83.1 |
| 700x28c | 28-622 | 2,130 | 83.9 |
| 700x32c | 32-622 | 2,155 | 84.8 |
| 700x40c | 40-622 | 2,205 | 86.8 |
| 650x47b | 47-584 | 2,130 | 83.9 |
| 27.5x2.25 | 57-584 | 2,193 | 86.3 |
| 29x2.2 | 56-622 | 2,306 | 90.8 |
| 29x2.4 | 61-622 | 2,337 | 92.0 |
| 26x2.1 | 54-559 | 2,095 | 82.5 |
| 20x1.75 | 47-406 | 1,571 | 61.8 |
Calculated values run 0.5–1.5% above a measured rollout; measure the rollout for best accuracy.
What Is the Bicycle Computer Circumference Calculator?
The Bicycle Computer Circumference Calculator is a tool that finds the wheel circumference to enter in a bike computer or sensor app. Speed and distance readings depend on that one number.
GPS bike computers use the circumference with a wheel-speed sensor in tunnels and under trees. A 1% circumference error gives a 1% speed and distance error.
Common Uses
This calculator has 4 uses: computer setup, sensor setup, trainer setup and accuracy checks.
- Set up computers: Enter circumference in mm.
- Set up speed sensors: Calibrate hub sensors.
- Set up trainers: Use the value for indoor speed.
- Check accuracy: Compare with a measured rollout.