Calculate bike gear ratio, gear inches and speed from chainring and cog teeth using typical wheel sizes, or compare a whole cassette in one gearing table.
How the Bike Gear Ratio Calculator Works
A single tooth ratio cannot show an entire drivetrain or compare bicycles with different wheel sizes. This calculator reports the ratio, gear inches, development and speed of one chainring and cog, or crosses each entered chainring with every entered cassette cog.
Comparison mode builds a chainring-by-cassette table for up to four chainrings and thirteen cogs. Reverse mode calculates the theoretical rear cog for target gear inches, rounds to the nearest whole tooth, and recalculates the nearest setup.
Formula and Method
Formula: ratio = chainring teeth / cog teeth; development = wheel circumference x ratio; gear inches = wheel diameter in inches x ratio
Speed follows from development x cadence x 60, with meters converted to kilometers or miles. Wheel diameter is derived from measured circumference divided by pi.
Choosing the Right Inputs
Enter comma-separated tooth counts stamped on the chainrings and cassette. Pick your wheel and tire size for a typical rollout, or choose Custom and enter the loaded circumference measured by rolling the bike one complete wheel revolution, then choose one cadence for the speed results.
| Chainring x cog | Ratio | Development |
|---|---|---|
| 34 x 34 | 1.000:1 | 2.105 m |
| 34 x 28 | 1.214:1 | 2.556 m |
| 50 x 17 | 2.941:1 | 6.191 m |
| 50 x 11 | 4.545:1 | 9.568 m |
Understanding Your Results
The gear ratio, the gear-inch range of the table, or the nearest whole rear cog leads. Every comparison row includes ratio, gear inches, development, and cadence speed; reverse mode includes nearest-cog metrics.
A larger ratio travels farther per crank revolution and demands more wheel torque from the rider. The complete table makes low gear, high gear, and intermediate steps visible together.
Worked Example
For 34 and 50 tooth chainrings with 11 and 17 tooth cogs, the tool returns four rows. The 50 x 17 row at 2,105 mm rollout is 2.941:1, 6.191 m, 77.6 inches, and 33.43 km/h at 90 rpm.
Common Mistakes
Do not enter cassette speed count instead of individual cog teeth, assume a nominal 700C or 29-inch label is the tire’s true diameter, or install a calculated cog without checking derailleur capacity and chain length.
Assumptions and Limitations
The table compares geometry, not drivetrain friction, tire slip, wind, grade, rider power, cross-chaining, chainline, or internally geared hub ratios. Reverse mode returns a theoretical and nearest whole cog, not a compatibility recommendation.
Sources
Sheldon Brown. Gain Ratios, Gear Inches and Meters Development, 2008 edition.
