Bike Gear Calculator
Enter your drivetrain and cadence to estimate gear ratio, gear inches, rollout, and speed.
What a gear calculator bike tool tells you
A gear calculator bike tool helps you understand how your drivetrain choices translate into real-world riding. Instead of guessing whether a setup is “easy enough for climbs” or “fast enough on flats,” you can calculate exact numbers and compare options quickly.
The most useful outputs are gear ratio, gear inches, rollout (distance traveled per crank revolution), and estimated speed at a target cadence. Together, these values tell you how hard each gear feels and how fast it can move the bike.
How to use this calculator
1) Enter chainring and rear cog teeth
Your chainring is the front sprocket. Your rear cog is the sprocket currently selected on the cassette. Larger front rings make gears harder; larger rear cogs make gears easier.
2) Enter wheel diameter
Wheel size changes rollout. Bigger wheels move farther per pedal turn in the same gear ratio. Typical examples include:
- Road 700c (roughly 26.5–27.5 inches depending on tire)
- 27.5-inch MTB
- 29-inch MTB
- 20-inch folding/compact bikes
3) Enter cadence
Cadence is how fast you spin the cranks, measured in RPM. Most efficient riding ranges from about 80–100 RPM, but this varies by rider, terrain, and riding style.
Meaning of each result
Gear ratio
Gear ratio is front teeth divided by rear teeth. A ratio of 3.0 means the rear wheel turns three times for each crank revolution (ignoring wheel circumference).
Gear inches
Gear inches combine ratio and wheel size into a single number. Historically popular with road and touring riders, gear inches are great for comparing setups across different bike types.
Rollout / development
Development is how many meters you travel for one full crank turn. This is especially useful for practical fit and pacing: higher development means more distance per pedal stroke.
Estimated speed
Speed is calculated from rollout and cadence in perfect conditions. Real speed varies due to gradient, wind, rolling resistance, rider position, and fatigue.
- Gear Ratio = Chainring Teeth ÷ Rear Cog Teeth
- Gear Inches = Gear Ratio × Wheel Diameter (in)
- Development (m/rev) = Gear Ratio × (π × Wheel Diameter in meters)
- Speed (km/h) = Development × Cadence × 60 ÷ 1000
Choosing gears for your riding style
Climbing and loaded touring
Lower gearing is your friend. Look for smaller chainrings, larger cogs, and lower gear inches. This improves comfort on long grades and reduces knee strain.
Road speed and group rides
You typically want a broad range: low enough for climbs, high enough for drafting and descents. Cadence-friendly steps between cogs make pace changes smoother.
Gravel and mixed terrain
Gravel riders benefit from versatile gearing because terrain changes constantly. A drivetrain with sufficient low-end gears can preserve energy over long days.
Quick benchmarks
- Under 30 gear inches: very easy climbing gears
- 30–70 gear inches: all-purpose utility range
- 70–100 gear inches: faster cruising and tempo riding
- 100+ gear inches: high-speed efforts and descents
Common mistakes when comparing bike gears
- Comparing tooth counts without considering wheel size
- Ignoring cadence preference and only looking at max speed
- Choosing large jumps in cassette spacing for performance riding
- Assuming one ideal setup works for every route
Final thoughts
A good gear calculator bike workflow helps you buy parts smarter and ride more comfortably. Use the tool above to test combinations before changing chainrings, cassette sizes, or wheel setups. Small drivetrain changes can make a big difference in climbing confidence, pedaling rhythm, and long-term performance.