Training / Cycling
Bike Gear Calculator: Ratios, Gear Inches, and Speed at Cadence
Enter your chainrings, cassette, wheel size, and cadence to get each gear's ratio, gear inches, distance per crank turn, and speed, with your top and lowest gears, the gear range, and the gain ratio.
Bike Gear Calculator: Ratios, Gear Inches, and Speed at Cadence: Each gear's ratio is chainring teeth ÷ cog teeth, and the distance per crank turn is that ratio times the wheel's circumference, worked out from the rim's bead seat diameter plus twice the tyre width. On 700 × 25c tyres, 50 × 11 covers 9.60 m per turn, 51.8 km/h at 90 rpm, and 34 × 28 covers 2.56 m, 13.8 km/h. Runs 100% locally in your browser with zero server file uploads.
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| Cog | 50-tooth ring | 34-tooth ring |
|---|---|---|
| 11 | 51.8 | 35.2 |
| 12 | 47.5 | 32.3 |
| 13 | 43.8 | 29.8 |
| 14 | 40.7 | 27.7 |
| 15 | 38 | 25.8 |
| 17 | 33.5 | 22.8 |
| 19 | 30 | 20.4 |
| 21 | 27.1 | 18.5 |
| 24 | 23.8 | 16.2 |
| 28 | 20.4 | 13.8 |
The gear ratio is chainring teeth ÷ cog teeth; times the wheel's circumference it gives the distance covered per turn of the cranks, and times the cadence, the speed. Gear inches are the ratio times the wheel diameter in inches, the old way of comparing gears. The gain ratio also counts the crank length: the wheel radius ÷ crank length × ratio, so it compares bikes with different wheels and cranks. Wheel sizes come from the rim's bead seat diameter plus twice the tyre width.
Example
A 50/34 chainset with an 11-28 cassette on 700 × 25c tyres spans 34 × 28 to 50 × 11, a gear range of 374%. At 90 rpm that is 13.8 to 51.8 km/h; a 34 × 32 low gear would make steep climbs easier at 12.1 km/h.
Wheel sizes
Wheels are named by the rim's ETRTO bead seat diameter: 622 mm for 700c and 29-inch, 584 mm for 27.5-inch, 559 mm for 26-inch. A wider tyre makes the wheel larger, so it raises every gear slightly.
How to use it
- Enter your chainrings and cassette cogs, such as 50/34 and 11-28.
- Choose the wheel and tyre size and set your cadence.
- Read the top and lowest gears and the table for every combination.
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Related tools
Frequently asked questions
What are gear inches?
The ratio times the wheel diameter in inches, a way of comparing gears from the days of penny-farthings: the diameter of the big wheel that one turn of the pedals would match. 50 × 11 on a road wheel is about 120 inches.
What is the gain ratio?
Sheldon Brown's measure: the distance the bike moves for each unit the pedal travels round its circle, so it allows for crank length as well as wheel size and gearing.
Why does my computer show a slightly different speed?
Real tyres flatten under load and vary by brand and pressure, so the rolling circumference is a little less than the calculated one; measure a roll-out for precision.
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