Bike Gear Ratio Speed Cadence Calculator

This calculator works out your bike’s speed from gear ratio and cadence. You enter your wheel diameter, chainring teeth, cassette teeth, and pedal cadence, and it returns your speed in km/h or mph, plus your gear inches and development (meters per pedal revolution).

Formula

The speed is calculated as:

Speed (km/h) = (Wheel diameter (m) × π × Chainring teeth ÷ Cassette teeth × Cadence (rpm) × 60) ÷ 1000

Where:

• Wheel diameter – the outer diameter of the wheel including tire, in inches (convert to meters by multiplying by 0.0254).
• Ï€ – approximately 3.1416, converts wheel diameter to circumference.
• Chainring teeth – number of teeth on the front gear (crankset).
• Cassette teeth – number of teeth on the rear gear (sprocket).
• Cadence – pedal revolutions per minute (rpm).
• 60 – converts minutes to hours.
• 1000 – converts meters to kilometers.

Gear inches = Wheel diameter (in) × Chainring teeth ÷ Cassette teeth. Development = Wheel circumference (m) × Chainring teeth ÷ Cassette teeth.

Worked Example

Using the default values: wheel diameter 27.5 in, chainring 44 teeth, cassette 16 teeth, cadence 80 rpm.

1. Convert wheel diameter to meters: 27.5 × 0.0254 = 0.6985 m.
2. Calculate wheel circumference: 0.6985 × π ≈ 2.194 m.
3. Calculate gear ratio: 44 ÷ 16 = 2.75.
4. Calculate development: 2.194 × 2.75 ≈ 6.034 m per pedal revolution.
5. Calculate distance per minute: 6.034 × 80 ≈ 482.7 m/min.
6. Convert to km/h: 482.7 × 60 ÷ 1000 ≈ 28.96 km/h.

The calculator shows 28.96 km/h, matching the example.

Why Gear Ratio and Cadence Matter

Cyclists use this calculation to plan gearing for different terrain. A lower gear (smaller chainring or larger cassette) makes pedaling easier but reduces speed at the same cadence. A higher gear does the opposite. Cadence is how fast you pedal; most recreational cyclists ride around 60–80 rpm, while racers often maintain 90–100 rpm. The product of gear ratio and cadence determines your speed, so a high gear at low cadence can equal a low gear at high cadence.

For example, a 44/16 gear at 80 rpm gives about 29 km/h. To go faster without pedaling faster, you could shift to a 50/16 gear – that gives about 33 km/h at the same cadence. Or you could increase cadence to 100 rpm on the same gear, reaching about 36 km/h. Understanding this trade-off helps you choose gears that keep your cadence in a comfortable range.

How to Choose the Right Gear Ratio

Selecting a gear ratio depends on your riding style, fitness, and terrain:

• Flat roads: higher gears (like 50/16 or 48/14) allow higher speeds at moderate cadence.
• Hills: lower gears (like 34/28 or 32/24) make climbing sustainable without overexerting.
• Commuting: a middle range (like 44/18) offers a balance for stop-and-go traffic.
• Track or time trial: fixed high gear to maintain speed on smooth surfaces.

Start with a gear that lets you maintain a cadence of 70–90 rpm on your typical route. If you find yourself grinding (cadence below 60), shift to an easier gear. If you’re spinning out (cadence above 110), shift to a harder gear.

Common Mistakes and Misconceptions

A frequent error is confusing wheel diameter with wheel circumference. The formula uses diameter, not the length around the tire. Another mistake is mixing units – if you measure wheel diameter in inches, you must convert to meters before calculating speed in km/h. Also, note that the gear ratio is chainring teeth divided by cassette teeth, not the reverse. Some riders think that a larger chainring always means faster, but that only holds if cadence stays the same; if you can’t push the harder gear, your speed may drop.

Another misconception is that gear inches directly measures speed. Gear inches is a legacy unit from penny-farthings – it represents the equivalent wheel diameter. A 70-inch gear means the bike would behave like a wheel of 70 inches in diameter. It’s useful for comparing gears, but not for speed calculation.

Limits of the Calculator

This calculator gives a theoretical speed based on constant cadence and no losses. Real-world factors reduce actual speed:

• Rolling resistance from tires.
• Air drag, which increases with the square of speed.
• Gradient (uphill slows you down, downhill speeds you up).
• Wind direction and speed.
• Friction in the drivetrain.
• Tire pressure and surface texture.

Also, wheel diameter changes with tire width and pressure. The calculator assumes a rigid wheel, but a loaded tire compresses slightly, reducing effective diameter. For most purposes, the error is under 2–3%.

Practical Uses

Cyclists use this calculator to:

• Set up a new bike or convert a single-speed.
• Compare gear options before buying parts.
• Estimate speed for a given cadence during training.
• Determine the right gear for a time trial or race.
• Plan a fixed-gear setup for commuting.

For example, if you want to ride at 25 km/h on flat ground with a cadence of 85 rpm, you can work backward to find the gear ratio. Using the formula, a 27.5-inch wheel needs a development of about 4.9 meters per revolution, which corresponds to a ratio of about 2.24 – so a 45/20 combination works.

Frequently Asked Questions

What is a good cadence for cycling?

Most recreational cyclists naturally pedal at 60–80 rpm. Competitive riders often train at 90–100 rpm to reduce muscle fatigue and improve cardiovascular efficiency. The optimal cadence varies by individual; a comfortable range that doesn’t strain your knees is best.

How do I measure my wheel diameter?

Look at the tire sidewall – it often lists the diameter in inches (e.g., 27.5, 29) or in ISO format (e.g., 622×42, where 622 mm is the bead seat diameter). For a rough measure, you can also roll the wheel one full turn and measure the distance traveled, then divide by π.

Does tire width affect speed?

Yes, but not through gear ratio. Wider tires have slightly larger overall diameter (if the rim is the same), which increases development. They also have higher rolling resistance, which reduces actual speed. The calculator accounts for the diameter change if you input the correct total wheel diameter.

What’s the difference between gear inches and development?

Gear inches is an old measure equal to wheel diameter × chainring/cog. Development is the distance traveled per pedal revolution in meters. Both describe the same relationship; development is more intuitive for metric users. Gear inches are still common in the US and UK.

Can I use this for a multi-speed bike?

Yes. For each gear combination (front chainring and rear cog), you can calculate the speed at a given cadence. This helps you understand the range of your bike and plan which gear to use on different terrain. The calculator works for any single combination at a time.

Why does my actual speed differ from the calculated speed?

Because the calculation assumes a perfect drivetrain, no wind, flat ground, and constant cadence. In reality, you slow down on hills, against wind, and when accelerating. Also, your cadence naturally varies. The calculated speed is a theoretical maximum for a steady effort.

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in wheel | Wheel diameter | in | 27.5 | 0
in chain | Chainring teeth | teeth | 44 | 0
in cog | Cassette teeth | teeth | 16 | 0
in cad | Cadence | rpm | 80 | 0
out speed | Speed | km/h | (wheel * 0.0254 * pi * chain / cog * cad * 60) / 1000 | 2
out gear_in | Gear inches | in | wheel * chain / cog | 1
out dev | Development | m | wheel * 0.0254 * pi * chain / cog | 2