How to use this calculator
- Enter or choose cadence.
- Enter or choose chainring teeth.
- Enter or choose rear cog teeth.
- Enter or choose wheel circumference.
- The speed updates as you type. Use Copy result or Share to keep it.
Method
Development (m) = Chainring ÷ Cog × Circumference (mm) ÷ 1000; Speed (km/h) = Development × Cadence × 60 ÷ 1000; Gear inches = Ratio × Circumference ÷ π ÷ 25.4
- Chainring, Cog
- teeth on the front and rear sprockets in use
- Circumference
- distance the wheel rolls in one turn
- Cadence
- crank revolutions per minute
Worked example
- Gear ratio = 50 ÷ 15 = 3.333.
- Development = 3.333 × 2.105 m = 7.017 m per crank turn.
- Speed = 7.017 × 90 × 60 ÷ 1000 = 37.89 km/h.
At 90 rpm in a 50×15 gear on a 2105 mm wheel you are riding at about 37.9 km/h (23.5 mph).
What the result means
Use the table to pick gears: if your comfortable cadence is 85–95 rpm, choose the gear that puts your target speed in that range.
Assumptions and limits
- No wheel slip and the chain is in the stated gear.
- Tyre pressure and load change the rolling circumference slightly.
Questions
What is a good cadence?
Most trained road cyclists settle between about 80 and 100 rpm on the flat; there is no single best value.
What are gear inches?
An old measure: the diameter of an equivalent penny-farthing wheel. Multiply by π for the distance travelled per crank turn in inches.