Gear to Speed Calculator (Cycling)
Enter chainring, cog, cadence, and wheel size to estimate real-time road speed.
What Is a Gear to Speed Calculator?
A gear to speed calculator estimates how fast a bike will travel for a given drivetrain setup and pedaling cadence. It connects the mechanical side of cycling (chainring and cassette teeth) to practical riding output (km/h and mph).
Whether you are training for road races, setting up a gravel bike, or comparing commuting gears, this tool helps you understand what each gear is actually doing on the road.
How This Calculator Works
Core Inputs
- Front chainring teeth: Number of teeth on your front ring.
- Rear cog teeth: Number of teeth on the selected rear sprocket.
- Cadence (RPM): How many crank revolutions per minute you pedal.
- Wheel diameter: Used to estimate wheel circumference if an exact circumference is not provided.
- Tire circumference (optional): If known, this gives more accurate speed estimates than wheel diameter alone.
Key Outputs
- Gear ratio: Front teeth ÷ rear teeth.
- Gear inches: A traditional cycling metric for mechanical advantage.
- Development: Meters traveled per pedal revolution.
- Wheel RPM: How fast your rear wheel spins.
- Speed: Estimated kilometers per hour and miles per hour.
Formula Reference
The calculator uses standard drivetrain math:
- Gear Ratio = Front Teeth / Rear Teeth
- Wheel Circumference (m) = Diameter(in) × 0.0254 × π (unless custom circumference is entered)
- Development (m/rev) = Wheel Circumference × Gear Ratio
- Speed (km/h) = Development × Cadence × 60 / 1000
- Speed (mph) = km/h × 0.621371
Example
Suppose you ride a 50/16 gear at 90 RPM with a 700c-style wheel close to 27 inches in diameter:
- Gear ratio = 50 / 16 = 3.125
- At 90 RPM, that translates to a fairly high wheel speed
- Estimated road speed is in the low-to-mid 40 km/h range, depending on exact tire circumference
This is why small changes in cadence or cog selection can significantly affect pace.
Using Results in Real Riding
Road Cycling
Use this calculator to plan pacing targets for flats, tempo rides, and time trial work. If your preferred cadence is 85–95 RPM, you can quickly find which rear cog supports your target speed without overgearing.
Climbing
On steep gradients, speed naturally drops and cadence tends to fall. Compare lower gears (for example, bigger rear cogs) to keep cadence in an efficient range and reduce muscular fatigue.
Commuting and Fitness
If your goal is consistency rather than max output, this tool helps identify a gear that keeps effort smooth in traffic, rolling terrain, or variable wind.
Important Real-World Factors
This is a clean mechanical estimate. Actual speed can vary because of:
- Wind resistance and rider position
- Road grade and surface quality
- Tire pressure and rolling resistance
- Bike load (bags, tools, water, accessories)
- Stop-start riding conditions
So treat results as a baseline for planning and comparison, not an absolute guarantee on every ride.
Frequently Asked Questions
Is wheel diameter enough, or should I enter tire circumference?
If you have measured circumference, use it. It is usually more accurate than an estimated diameter, especially across different tire widths and pressures.
What cadence should I use?
Many riders are most efficient between 80 and 100 RPM, but personal comfort, terrain, and training goals matter. Use your typical cadence first, then test alternatives.
Can I use this for e-bikes?
Yes. The drivetrain math is the same. Just remember that motor assistance changes how easy it feels to maintain a given cadence and speed.
Does this replace a bike computer?
No. A bike computer reports actual speed. This calculator predicts speed based on your chosen gear and cadence, which is ideal for planning and setup decisions.