Cycling
Bike Gear Calculator
Updated 11 Nov 2026 · Source: gear inches method, sheldonbrown.com ↗
Pick your chainring and cog tooth counts, your wheel and tire size, and a pedaling cadence. The calculator shows your speed, gear inches and the distance you travel per pedal turn.
Worked example
- Gear ratio 50 ÷ 17 = 2.941
- 2,105 mm wheel × 2.941 = 6.19 m per turn
- 6.19 m × 90 rpm × 60 = 33.4 km/h
Speed (mph) at 90 rpm on 700 x 25c
| Cog | 34 ring | 39 ring | 50 ring | 53 ring |
|---|---|---|---|---|
| 11 | 21.8 | 25.0 | 32.1 | 34.0 |
| 12 | 20.0 | 23.0 | 29.4 | 31.2 |
| 13 | 18.5 | 21.2 | 27.2 | 28.8 |
| 14 | 17.2 | 19.7 | 25.2 | 26.7 |
| 15 | 16.0 | 18.4 | 23.5 | 25.0 |
| 17 | 14.1 | 16.2 | 20.8 | 22.0 |
| 19 | 12.6 | 14.5 | 18.6 | 19.7 |
| 21 | 11.4 | 13.1 | 16.8 | 17.8 |
| 23 | 10.4 | 12.0 | 15.4 | 16.3 |
| 25 | 9.6 | 11.0 | 14.1 | 15.0 |
| 28 | 8.6 | 9.8 | 12.6 | 13.4 |
Gear ratio, gear inches and development
The gear ratio is simply chainring teeth divided by cog teeth. A 50-tooth ring with a 17-tooth cog gives 50 / 17 = 2.94, so the rear wheel turns 2.94 times for each turn of the pedals.
Ratio alone ignores wheel size, so riders use two other numbers. Gear inches is the wheel diameter in inches times the ratio; with the defaults it is about 77.6. Development is the wheel's rolling distance times the ratio, the ground you cover per pedal turn: about 6.19 m here.
- Higher gear inches or development: harder to push, faster at the same cadence.
- Lower numbers: easier to turn, better for steep climbs or heavy loads.
- Gain ratio goes one step further and also divides by crank length, for riders who want to compare crank sizes.
Wheel circumference matters more than you think
The calculator uses the rolling distance of the tire, not the rim size printed on it. Common values are 2,105 mm for 700 x 25c, 2,136 mm for 700 x 28c, 2,155 mm for 700 x 32c, 2,068 mm for 26 x 2.1 and 2,298 mm for 29 x 2.2.
Real tires often differ from chart values by 5 to 10 mm, depending on the make, width and pressure. That is small for gear choices but adds up over a long ride if your bike computer uses the wrong number.
Measure your own rollout
Pump the tire to your riding pressure and mark the spot where the valve touches the floor. Sit on the bike, or lean on it, and roll forward exactly one full wheel turn. Mark the floor again and measure the gap in millimeters.
That rollout is your real circumference. Enter it in your bike computer, and use the closest option here when you compare gears.
Turning a gear into a speed
Speed is development times cadence. At 90 pedal turns a minute, 6.19 m per turn is about 33.4 km/h, or 20.8 mph. The chart below lists speeds at 90 rpm on 700 x 25c tires for 34, 39, 50 and 53-tooth rings across cogs from 11 to 28.
Use it to check whether a cassette has a gear for your usual cruising speed, or how low your easiest climbing gear goes. For ride totals from distance and time, try the cycling speed calculator.
Comparing bikes with different wheels
Gear inches and development let you compare a road bike with a mountain bike fairly. A 29-inch wheel with the same ring and cog travels farther per pedal turn than a 26-inch wheel, so it feels like a harder gear.
The formulas behind every number are listed on our method page. If you train with a power meter, the watts per kg calculator puts your output in context.
Related pages
Questions
What is a good gear ratio for climbing?
There is no single answer; it depends on the hill, your fitness and your load. Lower gear inches make the pedals easier to turn, so a small ring with a large cog is the usual climbing setup.
What are gear inches?
Wheel diameter in inches multiplied by chainring teeth over cog teeth. A higher number means a harder gear that moves you farther with each pedal turn.
How fast is a 50 x 11 gear at 90 rpm?
About 32.1 mph on 700 x 25c tires, according to the chart.
How we calculate: every formula, with its author and year, is on our method page; data sources and their licenses are on sources.
gymnical.com gives estimates from published formulas and public data. It is not medical advice and not a training prescription. Last reviewed November 2026.