Health & Fitness
Bicycle Wheel & Tire Size Calculator
Updated Aug 27, 2026 Reviewed Aug 27, 2026
Calculate bicycle wheel diameter and circumference from ETRTO dimensions, use measured rollout, check bike-computer error and compare another tire size.
ETRTO, rollout and computer setup
Calculate actual wheel rollout
Result
Calculation summary
Enter values to see the result
Your result, breakdown, assumptions, and warnings will appear here.
Live wheel preview
One revolution sets distance and speed
Effective circumference
2,155 mm
Estimated diameter
686 mm
Computer error
-0.01%
The effective circumference drives revolution counts and reveals error in a stored bike-computer setting.
How to use this calculator
- 1Select a common wheel or enter the exact ETRTO width and bead-seat diameter.
- 2Use a loaded one-revolution measurement when available.
- 3Enter the bike-computer value and optionally compare another size.
Formula
C ≈ π × (BSD + 2W)
A measured rollout overrides the nominal formula for revolution and computer-error calculations.
Calculation steps
- Calculate nominal outside diameter.
- Choose estimated or measured circumference.
- Calculate revolutions, computer error and comparison differences.
Worked example
A 32-622 tire estimates to about 686 mm outside diameter and 2,155 mm circumference.
Assumptions
- Nominal width approximates tire height.
- Actual mounted size varies.
- Bead-seat diameters must match.
- Comparison does not prove compatibility.
Sources
Frequently asked questions
What does 32-622 mean?
Approximately 32 mm nominal width on a 622 mm bead-seat diameter.
Why measure rollout?
Pressure, load, rim and casing alter the effective rolling circumference.
How is computer error calculated?
Configured circumference divided by effective circumference determines the speed and distance scale.
Does equal diameter mean compatible?
No. Check bead-seat diameter, width, frame and component-maker requirements.
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