Bike Gear Calculator

What the bike gear calculator does

A bike's gears decide how hard or easy it is to pedal at a given speed, and this tool lays them all out so you can compare them. You give it the range of teeth on your chainrings and your cassette cogs, plus your wheel diameter, and it builds a table showing the gear ratio for every chainring and cog combination, so you can see your whole spread of gears at a glance.

It is the quickest way to understand what a drivetrain actually gives you: where your easy climbing gears are, where your fast gears are, and how evenly the steps are spaced in between.

How to use it

1. Enter your chainring range. The smallest and largest chainring tooth counts on your crankset.
2. Enter your cog range. The smallest and largest cog on your rear cassette.
3. Enter your wheel diameter in inches, which is needed to turn ratios into gear inches.

Press Calculate to build the table, or Reset to clear the fields.

Gear ratio, the core number

The gear ratio is simply the chainring teeth divided by the cog teeth:

Gear ratio = chainring teeth ÷ cog teeth

It tells you how many times the rear wheel turns for one full turn of the pedals. A 50-tooth chainring paired with a 25-tooth cog gives a ratio of 2.0, so the wheel spins twice for every pedal revolution. A bigger ratio is a higher, harder gear that carries you further per pedal stroke, good for speed and descents. A smaller ratio is a lower, easier gear that spins more freely, which is what you want for climbing.

Gear inches, comparing across wheels

Gear ratio alone does not account for wheel size, and a bigger wheel travels further per turn. Gear inches fix that by folding the wheel in:

Gear inches = gear ratio × wheel diameter

The result is an old but handy single number that lets you compare any two gears fairly, even on bikes with different wheels. A higher gear-inches figure means a bigger, harder gear. Most road gearing lands somewhere between about 30 gear inches at the easy climbing end and 120 or so at the fast end, which gives you a feel for where any particular gear sits.

An example with real numbers

Say you have a 50-tooth chainring, a 14-tooth cog, and a 27-inch wheel.

• Gear ratio = 50 ÷ 14 = 3.57
• Gear inches = 3.57 × 27 = about 96 gear inches

That is a tall, fast gear, the kind you would push on the flat or downhill. Compare it to a 34-tooth chainring with a 28-tooth cog: that is a ratio of 1.21, or about 33 gear inches, a low gear for grinding up a steep climb. Lining the two up shows the full range your drivetrain has to offer.

Reading your gearing table

Once the table is in front of you, a few things are worth looking for. Your highest and lowest numbers define your range: the high gears are for speed and the low gears for hills, and how wide that spread is tells you what terrain the bike is happy on. The steps between neighbouring gears matter too. Small, even steps let you fine-tune your effort and keep a smooth pedalling rhythm, while big jumps mean a noticeable change in effort with each shift. You will also spot overlaps, where a combination on the small chainring gives nearly the same ratio as one on the big chainring. That is completely normal and not wasted, it just means there is more than one way to reach a given gear. Reading all of this off the table helps you choose gearing that matches the riding you actually do.

Questions people ask

How do you calculate a bike gear ratio?

Divide the chainring teeth by the cog teeth. A 50-tooth chainring and a 25-tooth cog give a ratio of 2.0, meaning two wheel turns per pedal turn.

What are gear inches?

Gear inches are the gear ratio multiplied by the wheel diameter. They give a single number that compares gears fairly across bikes with different wheel sizes, where a higher number is a bigger, harder gear.

Which is the harder gear, high or low?

A high gear has a bigger ratio and is harder to push but carries you further per pedal stroke, for speed. A low gear has a smaller ratio and is easier to spin, for climbing.

Why do some gears overlap?

Because different chainring and cog combinations can produce nearly the same ratio. This is normal on any bike with multiple chainrings and simply means there is more than one way to get a given gear.

References

1. Sheldon Brown, Bicycle Gearing and Gear Inches (gear ratio and gear-inch definitions). https://www.sheldonbrown.com/gears/