Bicycle Gear Ratio Cadence Speed Calculator

This calculator works out your bike speed from gear ratio and cadence. You enter your wheel size, chainring teeth, cassette teeth, and pedal cadence, and it returns your speed in km/h or mph, along with the gear ratio in gear inches and meters of development. It uses the standard formula that connects drivetrain ratios to rolling speed.

Formula

The core relationship is: Speed = Wheel circumference × Gear ratio × Cadence. In symbols:

Speed (km/h) = (Wheel diameter (in) × 25.4 / 1000 × π × Chainring teeth / Cog teeth × Cadence (rpm) × 60) / 1000

Where:

• Wheel diameter – the actual outer diameter of the tire in inches (e.g., 27.5 for a 27.5-inch mountain bike tire, 29 for a 29er, 700c ≈ 27.5–28 depending on tire width).
• Chainring teeth – number of teeth on the front chainring (e.g., 44, 50, 34).
• Cog teeth – number of teeth on the rear cassette sprocket (e.g., 16, 11, 28).
• Cadence – pedal revolutions per minute (rpm). Typical recreational riding is 60–80 rpm; racers often spin 90–100 rpm.
• Ï€ ≈ 3.1416.

Gear inches (a classic measure) = wheel diameter × chainring / cog. Meters development = gear inches × 0.0254 × π.

Worked Example

Using the defaults: 27.5-inch wheel, 44-tooth chainring, 16-tooth cog, 90 rpm cadence.

1. Gear ratio = 44 / 16 = 2.75 (the rear wheel turns 2.75 times per pedal revolution).
2. Wheel circumference = 27.5 in × 25.4 mm/in = 698.5 mm = 0.6985 m; × π = 2.194 m.
3. Distance per pedal rev = 2.75 × 2.194 m = 6.034 m.
4. Per minute: 6.034 m × 90 rpm = 543.1 m/min.
5. Per hour: 543.1 × 60 = 32,586 m/h = 32.59 km/h.

The calculator shows 32.59 km/h, matching the steps above.

How to Choose Your Gear Ratio

The “right� ratio depends on your terrain, fitness, and what you want to achieve. Here are practical guidelines:

• Flat commuting or road riding: aim for a gear that lets you spin at 80–90 rpm at your desired speed. For a 700c wheel, that often means a ratio around 2.5–3.0 (e.g., 50/17 or 44/16).
• Climbing: you need a low gear (small chainring, large cog) to keep cadence up. A ratio below 1.5 (e.g., 34/28) is typical for steep hills.
• Fixed gear or single speed: pick a ratio that lets you pedal comfortably at your typical cruising speed without spinning out on descents. Many urban riders choose 2.5–3.0.
• Track racing: high ratios (3.0–4.0) favor speed over acceleration, but require strong legs.

Use the calculator to test different combos: change the cog teeth and see how speed changes at a fixed cadence. That’s the fastest way to understand your bike’s range.

Common Mistakes and Misconceptions

Mistake 1: Using nominal wheel size instead of actual tire diameter. A 700×23c tire is about 26.5 inches in diameter, not 29. Always measure your tire’s true outer diameter or use a tire size chart. A 1-inch error changes speed by roughly 3.5%.

Mistake 2: Confusing gear inches with meters development. Gear inches is a historical measure (diameter of an equivalent penny-farthing wheel). Meters development is the actual distance per pedal revolution. Both are shown in the calculator.

Mistake 3: Forgetting that cadence is per leg, not per wheel. One full pedal revolution = 360° of crank rotation. Your cadence is the number of crank revolutions per minute, which is what the formula uses.

Misconception: “Higher gear always means faster.� A higher ratio does increase speed at a given cadence, but if you can’t push it, your cadence drops and you go slower. Optimal speed comes from matching gear to your sustainable cadence.

How to Use the Result

The speed value is your theoretical speed at that cadence in that gear, assuming no losses from rolling resistance, wind, or drivetrain friction. In practice, actual speed will be slightly lower (often 2–5%) due to these losses. Use the result to:

• Compare gear combinations before buying a new chainring or cassette.
• Estimate your speed at different cadences to plan workouts.
• Check if your current gearing lets you maintain a comfortable cadence on your typical route.

For real-world speed, a bike computer or GPS is more accurate because it accounts for all losses and terrain.

Limitations of the Formula

The formula assumes a perfect, rigid wheel and no slippage. It ignores:

• Tire deformation and pressure (softer tires have slightly smaller effective circumference).
• Aerodynamic drag – at speeds above 20 km/h, drag becomes the dominant resistance.
• Rolling resistance and drivetrain friction.
• Gradient – climbing requires much more power at the same speed.

So treat the result as a “maximum possible� speed at that cadence. For planning, subtract 5–10% for realistic conditions.

Frequently Asked Questions

What is a good cadence for cycling?

Most recreational cyclists naturally pedal at 60–80 rpm. Competitive riders often prefer 90–100 rpm to reduce muscle fatigue and stress on knees. The “best� cadence is individual – experiment to find what feels efficient and sustainable for you.

How do I measure my wheel diameter?

The easiest way is to measure the outer diameter with a tape measure across the center of the tire. Alternatively, roll the wheel one full turn on the ground and measure the distance traveled – that’s your circumference. Divide by π to get diameter.

Does gear ratio affect speed or torque?

Yes, it trades one for the other. A higher gear (more chainring teeth or fewer cog teeth) gives more speed per pedal rev but requires more force. A lower gear gives easier pedaling (more torque at the wheel) but lower speed at the same cadence.

What’s the difference between gear inches and gear ratio?

Gear ratio is simply chainring teeth divided by cog teeth (e.g., 44/16 = 2.75). Gear inches multiplies that by the wheel diameter (27.5 × 2.75 = 75.6 inches). Gear inches is a traditional way to compare gearing across different wheel sizes.

How do I convert km/h to mph?

Multiply km/h by 0.621371. For example, 32.59 km/h ≈ 20.3 mph. The calculator gives km/h directly, but you can easily convert.

Can I use this for a mountain bike?

Yes, just enter your actual wheel diameter (usually 27.5 or 29 inches) and your chainring/cog teeth. The formula works for any bike with a standard drivetrain.

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in wheel | Wheel diameter | in | 27.5 | 0
in chainring | Chainring teeth | teeth | 44 | 0
in cog | Cassette cog teeth | teeth | 16 | 0
in cadence | Cadence | rpm | 90 | 0
out speed | Speed | km/h | (wheel * 25.4 / 1000 * pi * chainring / cog * cadence * 60) / 1000 | 2
out gear_in | Gear inches | in | wheel * chainring / cog | 1
out develop | Meters development | m | wheel * 25.4 / 1000 * pi * chainring / cog | 2