Bike Gear Ratio Calculator

The Bike Gear Ratio Calculator turns your chainring and cog teeth into the four numbers cyclists actually use to compare gears: gear ratio, gear inches, development (rollout), and gain ratio. It then estimates your speed at any cadence for your wheel or tyre size, draws an animated pair of gears, and plots how your speed changes as you spin faster.

What is a Bike Gear Ratio?

A gear ratio is simply the number of teeth on the front chainring divided by the number of teeth on the rear cog. It tells you how many times the rear wheel turns for one complete turn of the pedals. A 50-tooth chainring paired with a 15-tooth cog gives a ratio of 50 ÷ 15 = 3.33, meaning the wheel spins 3.33 times per pedal stroke. A bigger chainring or a smaller cog makes the gear harder and faster; a smaller chainring or a bigger cog makes it easier for climbing.

The Four Ways to Measure a Gear

Cyclists describe gearing in several complementary ways, and this calculator gives you all of them at once:

Gear Inches

Gear inches date back to the penny-farthing era: they express your gear as the diameter, in inches, of a giant direct-drive wheel that would move you the same distance per pedal turn. They make it easy to compare any drivetrain on a single scale, where higher means harder and faster.

Development (Rollout)

Development, or rollout, is the distance the bike travels for one pedal revolution, measured in metres (or feet). It is the most physical, intuitive measure: a 7-metre development means every pedal stroke carries you 7 metres down the road.

Gain Ratio

Gain ratio, devised by the late mechanic and writer Sheldon Brown, divides the wheel radius by the crank length and multiplies by the gear ratio. Because longer cranks give more leverage, gain ratio is the only measure that reflects how hard your legs actually have to push, making it the fairest way to compare bikes with different crank lengths.

How to Calculate Speed from Cadence

Once you know your development, your speed depends only on how fast you pedal:

For example, a 7-metre development at a cadence of 90 RPM gives 7 × 90 × 60 ÷ 1000 ≈ 37.8 km/h (about 23.5 mph). Raise your cadence and the speed rises in direct proportion, which is exactly what the speed-vs-cadence chart in the results shows.

Typical Gear Inches by Riding Style

What Affects Your Gearing?

How to Use This Calculator

1. Enter your chainring and cog teeth: Count the teeth on your front chainring and the rear cog you want to analyse.
2. Pick your wheel size and crank length: Choose a preset wheel/tyre size or enter a custom circumference in millimetres, then select your crank length.
3. Enter your cadence: Type the pedalling cadence (RPM) you want to estimate speed for — 90 RPM is a common road cadence.
4. Click Calculate: Read your gear ratio, gear inches, development, gain ratio and speed, watch the animated gears turn, and explore the speed-vs-cadence chart and step-by-step breakdown.

Frequently Asked Questions

What is a bike gear ratio?

A bike gear ratio is the number of teeth on the front chainring divided by the number of teeth on the rear cog. It tells you how many times the rear wheel turns for one full turn of the pedals. For example, a 50-tooth chainring with a 15-tooth cog gives a gear ratio of 3.33, so the wheel turns 3.33 times per pedal revolution.

What are gear inches?

Gear inches express your gearing as the diameter of an equivalent direct-drive wheel, like an old penny-farthing. It is the gear ratio multiplied by the wheel diameter in inches. Higher gear inches mean a harder, faster gear; lower gear inches mean an easier climbing gear. Typical road gears run from about 30 (very low) to 120 (very high) gear inches.

What is development or rollout?

Development, also called rollout or metres of development, is the distance the bike travels forward for one complete pedal revolution. It equals the gear ratio multiplied by the wheel circumference. It is an intuitive way to compare gears because it is measured directly in metres or feet of travel.

What is gain ratio?

Gain ratio, devised by Sheldon Brown, is the wheel radius divided by the crank length, multiplied by the gear ratio. Because it includes crank length, it reflects how hard you actually have to push and lets you compare gears fairly between bikes with different cranksets. It is a dimensionless number, typically between about 2 and 10.

How do I calculate speed from gear ratio and cadence?

Speed equals development (metres per pedal revolution) multiplied by cadence (revolutions per minute), multiplied by 60 and divided by 1000 to get kilometres per hour. For example, a development of 7 metres at 90 RPM gives 7 × 90 × 60 ÷ 1000 = 37.8 km/h. Divide by 1.609 to convert to miles per hour.

What is a good gear ratio for cycling?

It depends on the terrain. For climbing steep hills you want low gears (low gear inches), often a ratio near 1:1 or lower. For flat cruising a mid-range gear around 50 to 70 gear inches suits most riders, while fast riding and sprinting use high gears above 90 gear inches. Most geared bikes provide a wide range so you can pick the right gear for the moment.

Additional Resources

• Bicycle Gearing - Wikipedia
• Bicycle Performance - Wikipedia