Gear Cadence Speed Calculator: How to Use It

A gear cadence speed calculator works out your bike speed from your gear ratio and pedaling cadence. You enter your wheel size, gear teeth counts (chainring and cassette), and cadence in RPM, and it returns your speed in km/h or mph. This is useful for planning training targets, comparing gear setups, or estimating how fast you will go at a given pedaling rate.

Formula

The core formula is: Speed (km/h) = (Chainring teeth / Cassette teeth) × Wheel circumference (m) × Cadence (RPM) × 60 / 1000.

• Chainring teeth – number of teeth on the front chainring (e.g., 50).
• Cassette teeth – number of teeth on the rear sprocket (e.g., 15).
• Gear ratio – chainring teeth divided by cassette teeth. A 50/15 gives 3.33 – each crank turn moves the wheel 3.33 turns.
• Wheel circumference – calculated from wheel diameter (in inches) using Ï€ × diameter. Convert to meters by multiplying by 0.0254 (since 1 inch = 0.0254 m).
• Cadence – pedaling revolutions per minute (RPM).
• 60 and 1000 – convert minutes to hours and meters to kilometers.

The same formula works in miles per hour if you use wheel circumference in miles and adjust units.

Worked Example

Using the default values: chainring 50 teeth, cassette 15 teeth, wheel diameter 27.5 inches, cadence 90 RPM.

1. Gear ratio = 50 / 15 = 3.333
2. Wheel circumference in meters = 27.5 × 25.4 × π / 1000 = 27.5 × 0.0254 × 3.1416 = 2.194 m
3. Distance per crank turn = 3.333 × 2.194 = 7.313 m
4. Distance per minute = 7.313 × 90 = 658.2 m/min
5. Distance per hour = 658.2 × 60 = 39,492 m/h
6. Speed = 39,492 / 1000 = 39.49 km/h

The calculator shows 39.49 km/h (rounded to two decimals). That matches the formula output.

Why Cadence Matters

Cadence is how fast you pedal, usually measured in revolutions per minute (RPM). Most recreational cyclists pedal around 60–80 RPM; racers often train at 90–100 RPM. The same gear ratio gives a higher speed at higher cadence, but pedaling too fast or too slow affects efficiency and muscle fatigue. A gear cadence speed calculator helps you find a cadence that feels sustainable for your fitness and terrain.

How to Choose Your Inputs

To get an accurate speed, you need three correct numbers:

• Chainring teeth – look at the stamp on the crank arm or count the teeth. Common road bike chainrings are 50/34 or 52/36; mountain bikes often have 32 or 34.
• Cassette teeth – the largest and smallest sprockets are marked; for the gear you plan to use, count the teeth on that specific sprocket.
• Wheel diameter – this is the nominal wheel size (e.g., 700c ≈ 29 inches, 27.5 inches, 26 inches). For more precision, measure the actual wheel radius from axle to ground with the tire inflated, then double it.

If you don’t know your exact gear teeth, use the typical values from your bike’s spec sheet. The calculator is still useful for comparing relative speeds between gears, even if the absolute number is off by a few percent.

Common Mistakes and Limitations

• Using tire size instead of wheel diameter – a 700×25c tire has a diameter close to 29 inches, not 700 mm. Always use the outer diameter of the wheel, including the tire.
• Mixing units – if you enter wheel diameter in inches but expect speed in km/h, the formula must convert. The calculator above does that automatically.
• Ignoring drivetrain losses – real-world speed is slightly lower due to friction, wind resistance, and rolling resistance. The calculator gives theoretical speed, not actual ground speed.
• Cadence measurement – if you use a cadence sensor, make sure it reads crank revolutions, not wheel revolutions.

Comparing Gear Ratios

This calculator is handy when you are deciding between a compact (50/34) and standard (53/39) crankset, or choosing a cassette for climbing. For example, a 50/34 with a 11-28 cassette gives a low gear of 34/28 = 1.21, which is easier for hills than 39/25 = 1.56. You can also compute the speed at a given cadence for each gear and see the overlap between chainrings.

Alternatives and Real-World Measurement

If you want actual speed, a bike computer or GPS uses wheel speed sensors and does the same math in real time. Some cycling apps estimate speed from GPS without needing gear data. The calculator is most useful for planning – e.g., “If I pedal at 90 RPM on my 50/15, how fast will I go?� – before you ride. It also helps in training: set a cadence target and see what speed that corresponds to on a trainer.

Frequently Asked Questions

What is a good cadence for cycling?

Most recreational cyclists naturally pedal between 60 and 80 RPM. Competitive cyclists often train at 90–100 RPM for efficiency. A cadence below 60 RPM can strain muscles; above 100 RPM may cause bouncing. The best cadence depends on your fitness, terrain, and gear.

Does wheel size really affect speed?

Yes. A larger wheel covers more ground per revolution. For the same gear ratio and cadence, a 29-inch wheel gives about 5% more speed than a 27.5-inch wheel. That is why mountain bikes with smaller wheels feel slower on pavement at the same cadence.

How accurate is this calculator?

It is accurate to the mathematical relationship between gear, cadence, and wheel size. Real speed is lower because of wind resistance, tire rolling resistance, and drivetrain friction – typically 5–10% at moderate speeds. It is best used for comparing gears, not for precise speed records.

Can I use this for a single-speed or fixed-gear bike?

Yes. Single-speed bikes have one chainring and one cassette sprocket – just enter those numbers. Fixed-gear bikes are the same; the formula works regardless of whether you can coast.

What is the difference between gear inches and speed?

Gear inches is the diameter of an equivalent wheel in inches (chainring/cassette × wheel diameter). It is a relative measure of how hard a gear is. Speed adds cadence and time to give a real-world velocity. Gear inches is useful for comparing gears without calculating speed.

Related

• Bike Gear Ratio Calculator: How to Use It
• Bike Gear Range Calculator: How to Use It
• Bike Gear Ratio Calculator: How to Compare

in t | Chainring teeth | teeth | 50 | 0
in c | Cassette teeth | teeth | 15 | 0
in w | Wheel diameter | inches | 27.5 | 0
in cad | Cadence | RPM | 90 | 0
out speed | Speed | km/h | (t / c) * (w * 25.4 * pi / 1000) * (cad * 60) / 1000 | 2
out gain | Distance per crank turn | m | (t / c) * (w * 25.4 * pi / 1000) | 2