Bike gear ratio calculator
The gear ratio is 2.94: the wheel turns that many times for each turn of the pedals. That is a gear of 77.8 in, the bike moves 6.21 m per pedal turn, and the gain ratio is 5.81.
Result
Gear ratio
Gear inches
in
Development per pedal turn
m
Gain ratio
Wheel diameter with tire
mm
Wheel circumference
mm
How it works
A gear ratio only compares the two sprockets. How hard the gear feels also depends on the wheel, and a little on the cranks, so cyclists use three more measures. Gear inches multiply the ratio by the wheel diameter, which makes this a gear inches calculator as well. Meters of development is how far the bike rolls for one turn of the pedals. The gain ratio, which Sheldon Brown proposed, also counts the crank length, so this works as a gain ratio calculator when two bikes have different cranks. Use it for a single speed gear ratio or for any one gear of a geared bike; the bicycle gear ratio chart on the method page lists common chainrings and cogs side by side.
Formula
gear ratio = chainring teeth ÷ cog teeth. Wheel diameter = rim bead seat diameter + 2 × tire width (or roll-out ÷ π). Gear inches = wheel diameter in inches × gear ratio. Development = wheel circumference × gear ratio. Gain ratio = (wheel radius ÷ crank length) × gear ratio.
Worked example
The calculator opens with this example; the result above is computed from it.
| Input | Value |
|---|---|
| Chainring teeth | 50 |
| Cog teeth | 17 |
| Wheel size from | The size printed on the tire |
| Rim size | 622 = 700C, 29 inch |
| Tire width | 25 mm |
| Crank length | 170 mm |
| Gear ratio | 2.94 |
| Gear inches | 77.8 in |
| Development per pedal turn | 6.21 m |
| Gain ratio | 5.81 |
| Wheel diameter with tire | 672.0 mm |
| Wheel circumference | 2,111 mm |
Common cases
| Case | Starting values | Gear ratio | Gear inches | Development per pedal turn | Gain ratio | Wheel diameter with tire | Wheel circumference |
|---|---|---|---|---|---|---|---|
| Road bike, top gear | Chainring teeth 50; Cog teeth 11; Tire width 25 mm; Crank length 172.5 mm | 4.55 | 120.3 in | 9.60 m | 8.85 | 672.0 mm | 2,111 mm |
| Road bike, climbing gear | Chainring teeth 34; Cog teeth 32; Tire width 28 mm; Crank length 172.5 mm | 1.06 | 28.4 in | 2.26 m | 2.09 | 678.0 mm | 2,130 mm |
| Single speed commuter | Chainring teeth 44; Cog teeth 18; Tire width 32 mm; Crank length 170 mm | 2.44 | 66.0 in | 5.27 m | 4.93 | 686.0 mm | 2,155 mm |
| Mountain bike, lowest gear | Chainring teeth 32; Cog teeth 51; Tire width 60 mm; Crank length 170 mm | 0.63 | 18.3 in | 1.46 m | 1.37 | 742.0 mm | 2,331 mm |
| Folding bike with small wheels | Chainring teeth 50; Cog teeth 13; Tire width 35 mm; Crank length 170 mm | 3.85 | 63.4 in | 5.06 m | 4.74 | 419.0 mm | 1,316 mm |
Questions and answers
How do you calculate gear inches?
Multiply the wheel diameter in inches by the chainring teeth and divide by the cog teeth. With 50 teeth in front and 11 behind, on a wheel 672.0 mm across, the gear is 120.3 in, a ratio of 4.55.
What gear ratio does a single speed bike use?
A typical single speed commuter has 44 teeth on the chainring and 18 on the cog: a ratio of 2.44, or a gear of 66.0 in on a tire 32 mm wide. Adult single speed bikes usually sit between fifty-five and seventy-five gear inches.
What does meters of development mean?
It is the distance the bike travels for one full turn of the pedals. In a low mountain bike gear with 32 teeth in front and 51 behind that is 1.46 m, a ratio of 0.63.
Assumptions and limits
- The wheel diameter is the rim's bead seat diameter plus twice the tire width. A real tire is often a little smaller or larger than its marking, and it flattens under your weight, so expect a difference of a percent or two.
- The crank length changes only the gain ratio. Ratio, gear inches and development ignore it.
- Gear inches and development can be compared between bikes with different wheels. The plain ratio cannot.
- Tooth counts are whole numbers. Count them if the stamped number has worn off.
The result is an estimate for planning, not professional advice.
Sources
- Wikipedia: Bicycle gearing (definitions of gear inches, metres of development and gain ratio; wheel diameter is about the rim's 622 mm plus twice the tire width)retrieved 2026-10-13
- Sheldon Brown: Gain ratios (the three measures, with worked examples)retrieved 2026-10-13
- Prevelo: gear ratio, gear inches and gain ratio (formulas and a table of bikes)retrieved 2026-10-13
- Wikipedia: ISO 5775 (bead seat diameters of bicycle rims)retrieved 2026-10-13
Last updated:
Method in depth: Gear ratio, gear inches, development and gain ratio
Cite this page: Crank Math, “Bike gear ratio calculator”, https://crank-math.pages.dev/gearing/bike-gear-ratio-calculator/ (updated 13 October 2026).
Found a mistake? Email handycalc.sites+crankmath@gmail.com.