Bicycle Gear Calculator: Speed & Cadence

A bicycle gear calculator works out your speed from gear size and cadence, or the gear inches and development for any chainring and sprocket combination. You enter your wheel size, chainring teeth, sprocket teeth, and pedal cadence, and you get back your speed, gear inches, and meters of development. This page includes a simple speed-and-cadence calculator, then explains the formulas and how to use them for choosing gears.

Formula

The core formula for speed from cadence is:

Speed = (Wheel Diameter × π × Chainring Teeth ÷ Sprocket Teeth × Cadence × 60) ÷ 1000

Where:

• Wheel Diameter – outer tire diameter in inches (e.g., 27.5 inches for a 27.5″ mountain bike wheel, 29 inches for a 29er, 700c is about 27.5 inches with a road tire).
• Ï€ – approximately 3.14159.
• Chainring Teeth – number of teeth on the front chainring (e.g., 32, 50).
• Sprocket Teeth – number of teeth on the rear cassette sprocket (e.g., 16, 11).
• Cadence – pedal revolutions per minute (rpm).
• 60 – converts minutes to hours.
• 1000 – converts meters to kilometers.

Gear inches (a traditional measure) are simply:

Gear Inches = Wheel Diameter × (Chainring Teeth ÷ Sprocket Teeth)

Development (meters traveled per pedal revolution) is:

Development = Wheel Diameter × π × (Chainring Teeth ÷ Sprocket Teeth)

Worked Example

Using the defaults from the calculator: wheel diameter = 27.5 inches, chainring = 32 teeth, sprocket = 16 teeth, cadence = 90 rpm.

1. Gear ratio = 32 ÷ 16 = 2.0
2. Wheel circumference = 27.5 × π = 86.39 inches = 2.194 meters
3. Distance per pedal revolution = 2.194 m × 2.0 = 4.388 meters
4. Per minute: 4.388 × 90 = 394.9 meters/minute
5. Per hour: 394.9 × 60 = 23,694 meters/hour = 23.7 km/h

The calculator shows 23.7 km/h, gear inches of 55.0, and development of 4.39 meters. That matches.

How to Choose Your Gears

Choosing gears depends on your riding style, terrain, and fitness. Here are the main factors:

• Terrain: Hilly routes need lower gears (smaller chainring, larger sprocket) to climb without burning out. Flat routes allow higher gears for speed.
• Cadence preference: Most recreational riders pedal at 60–80 rpm, while racers often spin 90–100 rpm. Lower gears let you spin faster; higher gears force a slower, harder push.
• Speed goals: If you want to ride at 30 km/h on flat ground, you need a gear that gives that speed at your preferred cadence. Use the calculator to check combinations.
• Bike type: Mountain bikes have wide-range cassettes (e.g., 11–50 teeth) and small chainrings (30–34). Road bikes have compact (50/34) or standard (53/39) chainrings and tighter cassettes (11–28).

A common approach is to find your “flat road� gear: a gear that lets you ride at a comfortable speed at 80–90 rpm. Then have a few lower gears for climbs and a few higher for descents or tailwinds.

Common Mistakes and Misconceptions

Mixing units: The calculator uses inches for wheel diameter and gives speed in km/h. If you prefer mph, multiply the result by 0.621. If you measure your wheel in millimeters, convert to inches first (1 inch = 25.4 mm).

Using the wrong wheel size: Wheel diameter is not the rim size. A 700c rim with a 25mm tire is about 27.5 inches in total diameter, while a 29″ mountain bike wheel is actually about 29.0 inches with a typical tire. Check your tire sidewall for the exact outer diameter if you need precision.

Confusing gear inches with development: Gear inches is an old measure that ignores π, so it’s about 3.14 times smaller than development in meters. Don’t compare them directly.

Assuming cadence is constant: Your cadence varies with terrain and fatigue. The calculator gives a snapshot; real-world speed also depends on wind, rolling resistance, and gradient.

Limits of the Formula

The speed formula assumes no losses from friction, wind, or drivetrain efficiency. It also assumes a constant cadence. In reality, you can’t maintain 90 rpm up a steep hill, and on descents you might spin out. For planning purposes, the formula is accurate to within a few percent on flat ground with no wind.

Also, gear inches and development don’t account for crank arm length. A longer crank gives more leverage but doesn’t change the gear ratio. Some riders prefer to calculate “gain ratio� which includes crank length, but that’s beyond this simple calculator.

Alternatives to a Gear Calculator

If you don’t want to use a calculator, you can:

• Ride and feel: Shift through gears and find what feels comfortable at your typical speed. This is trial and error.
• Use a bike computer or app: Many GPS units show cadence and speed, so you can see your gear’s effect in real time.
• Consult a gear chart: Many bike shops have printed charts for common drivetrains. They give the same numbers as the calculator but are static.
• Try a gear ratio app: Some mobile apps let you input your drivetrain and see a visual gear graph.

Calculators are most useful when you’re planning a new drivetrain or comparing two bikes before buying.

Frequently Asked Questions

What is a good cadence for cycling? Most recreational cyclists naturally pedal at 60–80 rpm. Experienced riders often prefer 80–100 rpm for endurance. The “best� cadence depends on your muscle fiber type and the effort level; there’s no universal number.

How do I find my wheel diameter? Look on your tire sidewall for a number like “700x25câ€� or “27.5×2.1â€�. The first number is the rim size; the second is the tire width. For outer diameter, you can measure the wheel’s height with a tape measure, or use a standard chart: 700c road ≈ 27.5 inches, 29er MTB ≈ 29 inches, 27.5 MTB ≈ 27.5 inches, 26 MTB ≈ 26 inches.

What’s the difference between gear inches and development? Gear inches is the diameter of an imaginary wheel that would give the same gear ratio on a penny-farthing. Development is the actual distance you travel per pedal revolution. To convert gear inches to development in meters, multiply gear inches by 0.0254 × π (about 0.0798).

Why does my bike have so many gears if the ratio is just front divided by rear? The number of distinct ratios is the product of chainrings and sprockets, but many overlap. For example, a 2×11 drivetrain has 22 theoretical gears, but only about 15 unique ratios. The calculator helps you see which combinations are duplicates.

Can I use this calculator for a single-speed or fixed-gear bike? Yes. Just enter your one chainring and one sprocket. For a fixed gear, you might also want to know your speed at a given cadence for training, which this calculator provides.

Does crank length affect gear ratio? No, gear ratio is purely chainring/sprocket. Crank length affects torque and pedaling style but not the gear inches or speed for a given cadence. Some advanced metrics like “gain ratio� include crank length, but that’s not needed for most riders.

Related

• Cross Function in Cadence Calculator
• Critical Bench 1 Rep Max Calculator: How It Works
• Critical Swim Speed Calculator: Pace & Training Zones

in wheel | Wheel diameter | inch | 27.5 | 0
in cr | Chainring teeth | teeth | 32 | 0
in sp | Sprocket teeth | teeth | 16 | 0
in cad | Cadence | rpm | 90 | 0
out speed | Speed | km/h | (wheel * 0.0254 * pi * cr / sp * cad * 60) / 1000 | 1
out gear_in | Gear inches | inch | wheel * cr / sp | 0
out dev | Development | m | wheel * 0.0254 * pi * cr / sp | 2