Bike Gear Ratio Calculator

A gear ratio calculator tool converts the chainrings and cogs into numerical values so that a rider can compare gears. It shows the actual gear ratio, gear size (in inches), distance traveled per pedal revolution, and gear ratio.

By entering the parameters of the drive, these four data are displayed simultaneously, and it is calculated which speed can be maintained at a given pedal frequency. In addition, all sprockets are shown side by side so that the entire transmission ratio can be seen at a glance.

What does it mean to translate a bike?

If a chainring with 50 teeth is combined with a cog with 15 teeth, the gear ratio will be 3.33. For every revolution of the pedals, the rear wheel turns 3.33 times.

The larger the ratio is, the harder it is to pedal but at the same time higher speeds are achieved and more distance is covered per pedal stroke. The smaller the ratio is, the easier it is to pedal which makes it suitable for climbs. All other gear ratios listed on this page represent the same relationship in different ways.

Four ways to display a translation.

Cyclists rarely care about the pure gear ratio alone. This is because wheel size matters. Even with the same gear ratio, a smaller 20 inch wheel will result in a much easier ride than one with the same gear ratio mounted on a larger 700c road bike rim. These four figures each show different aspects that complement actual conditions.

Gearing inches" was a figure used on early bicycles with large wheels to indicate the diameter of a directly driven wheel that would give the same ratio. The "development" (distance traveled per pedal revolution) is the figure which most closely matches actual experience, as it indicates the actual distance traveled per pedal stroke.

The "translation ratio" is from Sheldon Brown. It takes into account the length of the crank, so that longer cranks give a greater leverage effect. This allows two bikes with different crank lengths to be compared fairly for the first time.

This is how this calculation tool works:

With each revolution of the pedals, the rear wheel turns according to the gear ratio and then moves forward because of its own circumference. The circumference of the wheel is calculated by adding twice the width of the tire to the rim diameter since tires rest on the edge of the rim both above and below.

Enter the number of teeth on your front chainring and rear cassette, select your wheel size and tire width. The gear ratio, gear inch rating, and development will be shown instantly. If you add cadence, you can calculate speed. Enable the gear ratio option if you want to include crank length in the calculation.

It is also possible to run the calculation in reverse. Enter your desired gear ratio into the "Gear Ratio" field and leave the sprocket or chainring fields blank. The calculator will then determine what number of teeth are required to achieve that gear ratio. If you have measured the circumference of the wheel, using the corresponding option will give you the most accurate results.

Calculation equation:

The translation and the parameters of the wheel determine all other values.

In this case, C_r and C_g stand for the number of teeth on the chainring or sprocket, D is the wheel diameter (ISO), W is the tire width, and C is the circumference of the wheel. The "Gear Inches", "Development" and "Speed" are all based on these two equations.

Here's an example for a road bike: A 50 tooth chainring, a 15 tooth cog and 700c wheels (with 25mm tires) are used with a cadence of 90 revolutions per minute and a crank length of 170 mm.

The result is that one pedal revolution covers a distance of 7.04 meters, the gear ratio is 6.59 and the speed is about 38.0 km/h or 23.6 mph. If you change to a sprocket with 12 teeth, at the same pedaling frequency of 90 rpm the speed will exceed 47 km/h. If you switch to a sprocket with 28 teeth, the speed returns almost to 20 km/h.

Understand the entire gear package

Individual sprockets give only a limited insight into overall gearing. A gearset is made up of a series of sprockets and the following table shows for each sprocket the ratio, inch pitch, development factor and speed, ordered from smallest heaviest to largest lightest sprocket.

Choose the smallest and largest cog that fits your cassette. For example, a typical road bike component will be suitable with 11 and 28 while modern mountain bike configurations with wide range gearing can use 10 and 52. The top row of the table gives the overall gear ratio. A 11 to 28 cassette has about a 2.55 difference between the easiest and hardest gears.

Choosing the right gear

A wide range of gears allows very low gears for climbing hills and very high gears for speed but the larger gap between cogs means a bigger change in cadence when changing gear. A narrow range has smaller gaps which gives more consistent cadence so is preferred on flat race courses.

The choice of chainring determines the overall range of gearing. A compact crankset for road bikes with 50/34 offers easier gears than a standard crankset with 53/39. This is one reason why many riders now use compact cranks. Checking out the maximum and minimum gear separately in a calculation tool will give you an idea of the overall range of gearing your bike can offer.

Tooth count

Many cassettes have the number of teeth on their surface, so you can count and note them once. When counting sprockets, it is easiest to identify the smallest and largest sprocket. By counting the sprockets at both ends of the cassette set, you determine the fastest and easiest gears.

The wheel size is usually indicated by the ETRTO number on the sidewall of the tyre. For example, for a 25-622 x 700 tyre, 622 is the required rim diameter for the calculator. If this is not known, roll the wheel once and measure the circumference, then switch to the manual entry option.

This calculator will show the ideal gear ratio for a chain drive. The actual speed depends on factors such as wind, incline, road surface and rider position so the speeds shown should be considered guidelines only. They do not guarantee that these speeds can be achieved in all conditions.