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Enter your chainring teeth and rear cog teeth, your wheel bead seat diameter in millimetres (622 for a 700c wheel) plus tyre width, your crank length, and your cadence in revolutions per minute. Wheel diameter is bead seat diameter plus twice the tyre width, converted to inches for gear inches and kept in millimetres for development. Gear ratio is chainring divided by cog. Gear inches multiply that ratio by wheel diameter in inches. Development, also called rollout or metres of development, multiplies the ratio by wheel circumference. Gain ratio divides wheel radius by crank length and multiplies by the gear ratio, giving a pure number that compares gears across different wheel sizes. Speed multiplies development by cadence and converts metres per minute into kilometres per hour and miles per hour.
Start with the gear ratio: a 50 tooth chainring driving a 17 tooth cog gives 50 divided by 17, or 2.94, meaning the wheel turns 2.94 times for each pedal revolution. Gear inches date back to penny-farthing wheels: multiply the ratio by wheel diameter in inches, so 2.94 on a 700c wheel with a 28 mm tyre, which measures 26.69 inches across, gives 78.51 gear inches. Development is the distance travelled per pedal revolution: the same gear gives 6.26 metres, because wheel circumference is pi multiplied by 0.678 metres, times the 2.94 ratio. Speed follows directly: 6.26 metres multiplied by 90 rpm multiplied by 60 minutes gives 33.8 km/h, or 21.0 mph. Gain ratio for that gear with 172.5 mm cranks is 5.78, meaning the bike moves 5.78 times as far as your foot travels around the pedal circle.
Step 1: count the teeth on your chainring and on the cog you want to check, or read them from the stamped numbers on the parts. Step 2: enter your wheel bead seat diameter, 622 mm for 700c, 584 mm for 650b, 559 mm for 26 inch, and 630 mm for 27 inch wheels, plus your measured tyre width, not just the printed size. Step 3: enter your crank length, usually printed on the inside of the crank arm, and your cadence, typically 70 to 100 rpm for most riders. Step 4: read all five outputs together: ratio for comparison, gear inches for feel, development for distance per revolution, gain ratio for cross-wheel comparison, and speed at your cadence for real-world meaning.
For any bicycle, the same steps apply whether it is a road, gravel, mountain, or city bike, and the meters of development figure is the same quantity as metres of development, written in US spelling.
A road compact setup, 50/34 chainrings with an 11-32 cassette on 700c with 28 mm tyres, spans from 121.3 gear inches at 50 by 11 down to 28.4 gear inches at 34 by 32, a gear range of about 428 percent. A gravel 1x setup, 40 teeth with a 10-44 cassette on 650b with 47 mm tyres, spans about 106.8 gear inches down to 24.3. A mountain bike 1x setup, 32 teeth with a 10-51 cassette on 29 inch wheels, spans about 93.7 down to 18.4 gear inches. A single-speed city setup near 50 by 17, giving 78.5 gear inches and 33.8 km/h at 90 rpm, sits in the flat cruising band, while a climbing gear near 34 by 32 at 28.4 gear inches lets a rider climb at walking pace without grinding to a halt.
This gear inches chart covers the most common setups, and the 50x17 example above is a useful reference point for flat cruising gears.
Under 30 gear inches feels very easy and suits loaded touring, steep mountain climbs, and crawling up gradients at low speed. From 30 to 50 feels easy and covers steady climbs and headwinds. From 50 to 70 feels moderate and covers rolling terrain and single-speed city riding. From 70 to 90 feels firm and covers flat cruising and fast group riding. Above 90 feels hard and suits sprints and descents. By bike type, road racing typically spans 70 to 110 gear inches, road endurance with a compact chainset 35 to 95, gravel and adventure 28 to 85, cross-country mountain biking 22 to 80, trail and enduro 18 to 70, touring and loaded bikepacking 20 to 80, and single-speed urban riding 55 to 75.
Comparing raw gear ratios across different wheels is misleading, because the same 3.00 ratio gives 49.5 gear inches on a small Brompton wheel, 79.4 on a 700c wheel with 25 mm tyres, and 87.9 on a 29 inch wheel with wide tyres. Tyre width alone matters too: moving from a 25 mm to a 32 mm tyre raises your gears by roughly 3 percent, because the wheel grows taller. That is why this calculator asks for bead seat diameter plus measured tyre width instead of a named wheel size, and why gain ratio exists: it removes wheel size from the comparison entirely, letting you judge whether a gear feels easy or hard on any bike. Always measure tyre width with calipers if you can, because printed sizes often differ from fitted sizes.
Single-speed riders pick one ratio for everything, so the choice matters more: 46 by 16, a ratio of 2.88, is a versatile starting point for mixed city riding, 48 by 16 suits flat ground, and 32 by 20 on a 29er suits off-road single-speed. Fixed gear riders add skid patches to the decision: the number of distinct skid patches depends on the greatest common divisor of chainring and cog teeth, and more patches spread tyre wear more evenly, which is why 44 by 17 is often preferred over ratios that share a large common factor. For fixed gear hills, aim near 60 to 65 gear inches, and for fixed gear speed, aim at 80 gear inches or higher. A 1x drivetrain gives a wide range with no front shifting and some overlap-free simplicity, a 2x drivetrain gives closer steps and a wider total range, and a 3x drivetrain gives the widest range of all, near 604 percent on a classic trekking setup, at the cost of more overlapping gears.
The most common mistakes are comparing ratios across different wheels, ignoring tyre width, assuming more gears means a wider range, cross-chaining small to small or large to large, and choosing gearing from flat-road riding alone. Choose your lowest gear for your steepest real climb at your real climbing cadence, not for a flat test ride: at 70 rpm, the gear inches you need roughly equal your climbing speed in mph multiplied by 4.8, so 5 mph needs about 24 gear inches. Choose your highest gear for your fastest regular descent or sprint, then check the steps between gears feel even. Beginners should favour lower gears and closer steps over a tall top gear they rarely use.
Divide chainring teeth by cog teeth: 50 divided by 17 equals 2.94. That number means the wheel turns 2.94 times for each full pedal revolution.
Gear inches are the gear ratio multiplied by wheel diameter in inches, a number inherited from penny-farthing wheel sizes. It lets you compare how hard a gear feels across different bikes, unlike the raw ratio alone.
Multiply the gear ratio by wheel diameter in inches, where wheel diameter equals bead seat diameter plus twice the tyre width, divided by 25.4. For 50 by 17 on 700c with 28 mm tyres, that is 2.94 times 26.69, or 78.51 gear inches.
Gear ratio compares teeth only and ignores wheel size, while gear inches include wheel diameter, so the same ratio feels much easier on a small wheel than on a large one. Use gear inches or gain ratio when comparing gears across different bikes.
Gear inches are a scaled diameter in inches, while development, or rollout, is the actual distance travelled per pedal revolution in metres or feet. They describe the same gear in different units: development equals gear inches converted through wheel circumference.
Gain ratio is wheel radius divided by crank length, multiplied by the gear ratio. It is a pure number that compares gears across any wheel and crank combination, and a street-use gain ratio near 5 to 5.3 suits many riders.
Multiply development in metres by cadence in rpm by 60 and divide by 1,000 for km/h. For 50 by 17 on 700c at 90 rpm, development is 6.26 metres, giving 33.8 km/h, or 21.0 mph.
Aim for a lowest gear near 1.0 or lower in ratio terms, roughly 27 gear inches or below, so you can climb steep gradients at a sustainable cadence. On a compact road setup, 34 by 32 at 28.4 gear inches is a practical climbing gear.
A compact chainset such as 50/34 with a wide cassette such as 11-32 gives a forgiving range from easy climbing gears to fast flat gears, with closer steps than a very wide 1x setup. Favour low gears you will actually use over a tall top gear.
For mixed city riding, 46 by 16 is a versatile starting point, 48 by 16 suits flat ground, and lower ratios such as 44 by 17 suit hills. For fixed gear riding, also consider skid patches, which spread tyre wear when chainring and cog share little common factor.
It is the tooth count of the two chainrings on a 2x crankset: 50 teeth on the large ring and 34 on the small ring, or 48 and 35. The large ring pairs with smaller cogs for speed, the small ring with larger cogs for climbing.
Enter the bead seat diameter, 622 mm for 700c, plus your measured tyre width, rather than a named size alone. A 700c wheel with 25 mm tyres measures about 26.4 inches across, while the same rim with 32 mm tyres measures larger and raises your gears.
Yes: moving from 25 mm to 32 mm tyres raises gears by roughly 3 percent, and the same ratio on a small wheel versus a 29 inch wheel can differ by nearly 40 gear inches. Measure fitted tyre width where possible, because printed sizes often differ.
Longer cranks give more leverage for the same gear, which gain ratio captures by dividing wheel radius by crank length. Changing crank length alone changes gain ratio without changing gear ratio or gear inches, so it matters for feel, not for speed at a given cadence. In short, the crank length effect on gain ratio is direct: longer cranks lower the gain ratio for the same gear, because your foot travels a larger circle for the same wheel movement.
Most riders settle between 70 and 100 rpm, with 90 rpm a useful default for calculations. Climbing cadence is often lower, near 70 rpm, so check your lowest gear at 70 rpm, not at 90 rpm, when judging hill gearing.
Count the teeth around one cog, or read the stamped number on the cog or cassette lockring. Count chainring teeth the same way, and double-check the cog you actually ride in most, not just the largest or smallest.