Bike Gear Ratios Explained: Chainring, Cog, Wheel and Cadence

A bike’s gear ratio is chainring teeth ÷ cog teeth, and from it you get how far the bike travels with one full turn of the pedals. With a 50T chainring, a 17T cog and 28 mm road tires, that’s 78.3 gear inches, or 6.25 m per pedal stroke; if you pedal at 90 revolutions per minute, you’re doing 21 mph (33.7 km/h). With the 34x34 on a modern road bike you drop to 26.6 gear inches (2.12 m), and at the same 90 rpm you’re doing 7.1 mph (11.5 km/h), just enough for a steep climb.

With three numbers (chainring, cog and wheel) you know how fast each gear goes, whether you’re short on low gears for climbing and whether you have tall gears you never use. Below are the formulas, the tables and how to read them. If you’d rather skip the math, the gear ratio calculator builds the full table for your bike.

What gear ratio means

Each time you turn the cranks, the chainring pulls the chain as many links as it has teeth. The chain turns the rear cog, and since the cog is smaller, it turns more than once. That proportion is the gear ratio:

Gear ratio = chainring teeth ÷ cog teeth

A 50x17 has a ratio of 50 ÷ 17 = 2.94: for every pedal stroke, the rear wheel turns 2.94 times. To turn that into distance, there are two common ways:

Gear inches = ratio × wheel diameter (in)

Development (m) = ratio × wheel circumference (m)

A road wheel has a 622 mm rim bead seat diameter (the number in the ETRTO size, such as “28-622”; ETRTO is the European standard that sets those dimensions). With a 28 mm tire, the outside diameter is about 676 mm, or 26.6 in, and the circumference about 2,125 mm (83.7 in). So:

• 50x17 → 2.94 × 26.6 = 78.3 gear inches (6.25 m)
• 50x11 → 4.55 × 26.6 = 121.0 gear inches (9.66 m)
• 34x34 → 1.00 × 26.6 = 26.6 gear inches (2.12 m)

Note that none of this depends on crank length or on how strong you are: it’s pure geometry. What crank length changes is leverage, and we cover that below with the gain ratio.

Ratio, gear inches, development and gain ratio

The same idea is expressed in four ways. In the U.S. and the U.K., riders talk in gear inches or simply name the combination (“I climbed it in the 34x28”). In Spain, France and Italy they use meters of development: how far the bike rolls per pedal stroke. And engineer and mechanic Sheldon Brown proposed the gain ratio, which divides the wheel radius by the crank length and multiplies by the ratio: how far the bike travels for each unit of distance the pedal travels.

This table shows typical combinations with 700x28 tires and 172.5 mm cranks:

To compare bikes with different wheels, gear inches or meters are the practical choice. Gain ratio only adds something when you change cranks: with the same 50x17, going from 172.5 to 170 mm raises the gain ratio from 5.77 to 5.85, so the gear “feels” 1.5% harder because the lever is shorter. If you’re unsure about your crank length, see the crank length calculator.

Cadence and speed

Cadence is how many times you turn the pedals per minute (rpm). From gear inches and cadence you get speed:

Speed (mph) = gear inches × cadence (rpm) ÷ 336

For example, 78.3 × 90 ÷ 336 = 21.0 mph. The same gear at 60 rpm gives 14.0 mph. (In metric: development in meters × rpm × 60 ÷ 1,000 = km/h.) This table, with 700x28 tires, sums up speeds at three common cadences (more gears and cadences in the speed by cadence chart):

What’s a “good” cadence? There isn’t just one, but there is a useful reference: a study by Lucía, Hoyos and Chicharro of pro riders in the Giro, the Tour and the Vuelta measured about 89 rpm on flat stages, 92 rpm in time trials and about 71 rpm on climbs. For most amateurs, riding at 80-95 rpm on the flat and not dropping below 70-75 rpm on climbs is a good rule. Below that, every pedal stroke takes a lot of force and your knees feel it on a long climb.

Tip: if your tallest gear already gets you past 30 mph at 90 rpm, you have more than enough for the flat. What’s usually missing is low gears.

Speed depends on the watts you put out, not just the gear. To find out how fast you’d go with your power on the flat or climbing, use the power and speed calculator.

Chainring × cog chart: 50/34 with 11-34

This is one of the best-selling road setups: a 50/34 compact crankset and a 12-speed 11-34 cassette (the cogs on a 12-speed Shimano 105 are 11, 12, 13, 14, 15, 17, 19, 21, 24, 27, 30 and 34; each groupset’s cassettes are in the guides to Shimano road groupsets and SRAM groupsets). Gear inches and speed at 90 rpm with 700x28 tires:

Three things the chart tells you:

1. Many gears overlap. There’s no 50x25 on this cassette, but the 50x24 (55.5 in) and the 34x17 (53.3 in) are almost the same, as are the 50x19 (70.1 in) and the 34x13 (69.6 in). Of the 24 combinations, once you remove the cross-chained ones and those less than 4% apart, about 17 distinct gears are left.
2. Cross-chained gears run the chain at a steep angle: big ring with the biggest cogs, or small ring with the smallest. They work, but they create more friction, make noise and wear faster. And they always have an equivalent on the other chainring.
3. The total range goes from 26.6 to 121 gear inches: the tallest gear is 4.55 times the lowest. That covers almost everything, from 10% pitches to descents at over 30 mph. If you’re torn between one and two chainrings, we compare them with numbers in 1x vs. 2x: which drivetrain to choose. For other chainrings and cassettes, see the gear development chart or print the gear chart to keep in your workshop.

How the wheel affects your gears

The tire changes the diameter, and with it every gear. The effect is small on road bikes and significant between types of bikes:

Between a 25 mm and a 40 mm tire there’s a 4% difference: your gravel 34x34 is a little taller than the same 34x34 on a road bike. A 29er with 2.25 in (57 mm) tires gains just over 8% compared with a 700x28, which is why mountain bikes run cassettes with 51- or 52-tooth cogs. For the exact circumference of your tire, use the tire size calculator.

How to calculate your bike’s gear ratios

1. Count your chainring teeth. They’re usually stamped on the chainring itself or the crank (50-34, 48-31, 40…).
2. Check the cassette. The range (11-34, 10-44…) is printed on the largest cog or the lockring. If you don’t know the cogs in between, count them or look them up on the manufacturer’s spec sheet: two 11-34 cassettes can be spaced differently.
3. Read the tire size on the sidewall (“28-622”, “700x28c”, “29x2.25”).
4. Work out your lowest and tallest gears. Small ring with the biggest cog, and big ring with the smallest cog. They tell you whether you’ll climb comfortably and whether you’ll spin out on descents.
5. Compare with your cadence. Calculate speed at 90 rpm for the flat and 70-75 rpm for climbs. If your lowest gear, climbing at your pace, drops you below 70 rpm, you need lower gearing. We go into it in depth in the best gear ratio for climbing.

Common mistakes

• Comparing teeth only. A gravel 34x34 with a 45 mm tire and a road 34x34 with a 25 mm tire aren’t the same gear: there’s more than a 5% difference. Compare in gear inches.
• Thinking more speeds means more range. A 12-speed 11-34 has the same range as an 11-speed 11-34; what you gain is smaller jumps between cogs.
• Focusing on the tallest gear. Almost nobody uses a 53x11 (128 gear inches, 34.4 mph at 90 rpm). When you buy, look at the lowest gear first.
• Riding cross-chained all the time. If you’re always in the 50x30 or 34x11, switch chainrings: there’s an almost identical gear with a straight chain line, and your chain and cogs will last longer. To know when it’s time to replace your chain, see when to replace your chain.
• Forgetting the chain when you change cassette or chainrings. If you move to a bigger cog, you’ll probably need more links: check with the chain length calculator.

Updated October 19, 2026 ·Report an error on this page