⚙️ Bike Gear Ratio Calculator

Understanding your gear ratio result

Gear-inch ranges below are general, widely used conventions from cycling gearing guides, not strict scientific thresholds — appropriate gearing always depends on terrain, rider fitness and preferred cadence.

• Gear ratio is a dimensionless number, while gear inches and development express the same gearing relative to a specific wheel and tire size — the same gear ratio produces different real-world speeds on different wheel sizes.
• The default wheel circumference of 2096 mm approximates a common 700×25c road tire; other tire widths and wheel sizes have different circumferences, which should be entered for an accurate result.
• A gear's practical usefulness depends heavily on the cadence at which it is comfortably pedaled — comparing gear inches without considering cadence gives an incomplete picture of the resulting speed or effort.
• The gear-inch ranges shown are general cycling conventions, not authoritative or medically validated thresholds, and suitable gearing varies by terrain, fitness and riding style.

What is a bicycle gear ratio?

A bicycle's gear ratio is the number of chainring teeth divided by the number of cog (rear sprocket) teeth, representing how many times the rear wheel turns for each full pedal revolution. A higher ratio means the wheel turns more per pedal stroke — a 'harder' gear that produces more speed per revolution but requires more force to turn.

Because gear ratio alone does not account for wheel size, cyclists commonly convert it into 'gear inches' — a traditional unit dating back to penny-farthing bicycles, representing the diameter of an equivalent-sized direct-drive wheel that would produce the same distance per pedal revolution. This makes gearing comparable across bikes with different wheel and tire sizes.

'Development' expresses the same idea in metric distance terms: the number of metres the bicycle travels per full crank revolution. Multiplying development by cadence (revolutions per minute) gives the resulting speed.

How to use this gear ratio calculator

1. Enter the number of teeth on your chainring (front) and cog (rear sprocket).
2. Enter your wheel's rolling circumference in millimetres — the default of 2096 mm approximates a common 700×25c road tire; adjust it for your specific tire size if known.
3. Enter your pedaling cadence in revolutions per minute (rpm).
4. Read your gear ratio, gear inches, development (metres per crank revolution) and the resulting speed.

The formula behind gear ratio calculations

Gear ratio is simply chainring teeth divided by cog teeth. Gear inches multiplies this ratio by the wheel diameter in inches, derived from the entered circumference. Development converts the ratio and circumference into metres traveled per crank revolution, and speed multiplies development by cadence.

Worked example: a 50-tooth chainring with a 25-tooth cog gives a gear ratio of 50 ÷ 25 = 2.0. With a wheel circumference of 2096 mm (wheel diameter ≈ 26.4 in), this is about 52.8 gear inches and a development of 2.0 × 2.096 ≈ 4.19 m per crank revolution. At a cadence of 90 rpm, this produces a speed of roughly 2.0 × 2096 × 90 × 60 ÷ 1,000,000 ≈ 22.6 km/h.

Wheel circumference varies with tire size, tire pressure and rider weight, so entering an accurate circumference for your specific setup — measured by rolling the wheel one full revolution, if precision matters — improves the accuracy of gear inches, development and speed figures.

Common mistakes

• Confusing gear ratio (a dimensionless number) with gear inches (a size measurement dependent on wheel and tire circumference).
• Using a generic wheel circumference default when a specific tire size or pressure meaningfully changes the actual rolling circumference.
• Comparing gear inches between bikes with very different wheel sizes without recognizing that the same gear inches figure produces the same effective gearing regardless of wheel size — that is the point of the unit.
• Ignoring cadence when comparing 'faster' or 'harder' gears — a numerically higher gear ratio only produces more speed if it can actually be pedaled at a comparable cadence.
• Assuming gear-inch ranges for 'climbing' or 'cruising' gears are fixed scientific cutoffs rather than general, terrain- and rider-dependent conventions.

Questions fréquentes

Références

1. Sheldon Brown Cyclery (maintained by John Allen). Glossary of Bicycle Terms — gear ratios, gain ratios and gear inches. sheldonbrown.com.
2. International Cycling Union (UCI) and general bicycle-mechanics references on drivetrain gearing conventions.