About the Bike Gear Calculator
This bike gear calculator shows what a chainring and cog combination really means on the road or trail. Enter the teeth on your front chainring and rear cog, choose a wheel and tire size, and set your pedalling cadence to get the gear ratio, gear inches, metres of development, gain ratio and your speed in mph and km/h.
Road cyclists use it to compare compact and standard chainsets or pick a cassette for a hilly sportive, gravel and mountain bikers to find a low enough climbing gear, and single-speed and fixed-gear riders to choose one ratio that works everywhere. Paste your whole cassette to see every gear side by side with the speed each one gives at your cadence.
Wheel circumferences are typical rolling values from bike-computer tire charts; your exact tire, pressure and rider weight change them slightly. For the most accurate speed, measure one wheel roll-out on the ground in millimetres and enter it as a custom circumference.
With the default inputs, the speed at cadence is 20.8 mph. Change any value above to recalculate instantly.
How to use the bike gear calculator
- 1Enter the teeth on your chainring and the rear cog you want to check.
- 2Choose your wheel and tire size, or enter a measured circumference.
- 3Set a typical cadence — 80–95 rpm is common on the road.
- 4Optionally paste your cassette cogs to compare every gear.
- 5Read speed, gear inches and development, and use the table to plan your gearing.
Formula and method
The gear ratio is how many times the rear wheel turns for each full turn of the pedals. Gear inches, the traditional English measure, multiplies that ratio by the wheel’s effective diameter in inches (circumference ÷ π ÷ 25.4). Development, used in Europe, is the distance travelled per pedal revolution in metres.
Speed is development multiplied by cadence (revolutions per minute) and 60 minutes, converted to km/h and mph. Gain ratio, proposed by Sheldon Brown, also accounts for crank length: it is the distance the bike travels divided by the distance your foot travels in the pedal circle, so it compares gearing fairly across different crank lengths and wheel sizes.
- Chainring / Cog
- Number of teeth on the front ring and rear sprocket
- Circumference
- Rolling circumference of the tire (mm)
- Cadence
- Pedal revolutions per minute
- Crank length
- Distance from bottom bracket to pedal axle (mm)
Worked examples
Road bike 50/17 on 700×25c at 90 rpm
The ratio is 50 ÷ 17 = 2.94. With a 2,105 mm tire each pedal turn covers 6.19 m, so at 90 rpm you travel 6.19 × 90 × 60 = 33.4 km/h, or 20.8 mph. That is about 77.6 gear inches.
Mountain bike climbing gear 34/34 on 29 × 2.3 at 80 rpm
A 1:1 gear moves the bike one wheel circumference (2.326 m) per pedal turn. At 80 rpm that is 11.2 km/h or 6.9 mph — a typical low climbing gear of about 29 gear inches.
Fixed gear 48/16 on 700×28c at 100 rpm
A 3:1 ratio on a 2,136 mm tire gives 6.41 m per pedal turn. Spinning at 100 rpm yields 38.4 km/h (23.9 mph), with about 80 gear inches.
Frequently asked questions
What is a good gear ratio for a road bike?+
Most riders want a top gear around 100–125 gear inches for descents and a bottom gear of 30–40 gear inches for steep climbs. A compact 50/34 chainset with an 11–32 cassette covers roughly 28–120 gear inches on 700×25c tires.
What are gear inches?+
Gear inches express a gear as the diameter of an equivalent direct-drive wheel, as on an old penny-farthing. Multiply the gear ratio by the wheel diameter in inches; higher numbers are harder gears.
What cadence should I ride at?+
Many road cyclists settle between 80 and 95 rpm, while beginners often pedal at 60–75 rpm. Higher cadences reduce the force on each pedal stroke and can delay leg fatigue.
How do I measure my wheel circumference?+
Mark the tire and the ground, roll the bike forward one full wheel revolution with your weight on it, and measure the distance in millimetres. This roll-out is more accurate than any chart value.
Is a bigger chainring or a smaller cog harder to pedal?+
Both make the gear harder. Increasing chainring teeth or decreasing cog teeth raises the ratio, so each pedal stroke moves you further but needs more force.
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