What this calculator does
A bicycle gear is the ratio of front chainring teeth to rear sprocket teeth. A 50 tooth chainring with an 11 tooth sprocket is 4.55:1, meaning the wheel turns four and a half times for every turn of the pedals.
Development is the more useful figure: how far the bike travels per pedal revolution. That 50/11 combination on a 700c wheel gives exactly 10 metres per crank turn, which at 90 rpm is 54 km/h. Gear inches is an older measure of the same thing, expressing the gear as the diameter a direct-drive penny-farthing wheel would need to be.
The formula
The gear ratio is the chainring teeth divided by the sprocket teeth. Development is the wheel circumference, π times the diameter, multiplied by that ratio. Speed is development multiplied by cadence, converted to km/h. Gear inches is the wheel diameter in inches multiplied by the ratio, which is why the numbers look large.
| Term | Meaning |
|---|---|
| Gear ratio | Chainring teeth divided by sprocket teeth. Higher is a harder gear. |
| Development | Distance travelled per pedal revolution, in metres. The most directly meaningful measure. |
| Gear inches | Wheel diameter multiplied by the ratio, an older measure dating from direct-drive bicycles. |
| Cadence | Pedal revolutions per minute. 80 to 100 rpm is a common range for trained riders. |
The inputs explained
| Field | What to enter |
|---|---|
| Chainring teeth | Front chainring teeth. |
| Rear cog teeth | Rear sprocket teeth. |
| Wheel diameter (mm) | Wheel diameter in millimetres including the tyre. 700c road wheels are about 700 mm, hence the name. |
| Cadence (rpm) | Cadence in pedal revolutions per minute. |
When to use it
Comparing gear setups
Two drivetrains with different chainrings and cassettes are hard to compare on the numbers alone, and converting both to development or gear inches makes them directly comparable.
Choosing a cassette for terrain
A wider-range cassette trades top-end speed for a lower climbing gear, and seeing the speeds at each end quantifies the trade.
Checking for gear overlap
A double chainring setup often has several combinations that produce nearly identical ratios, which is duplicated effort the calculator exposes.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What speed does each sprocket give?
A fixed chainring and cadence across a range of rear sprocket sizes.
| Rear sprocket | Speed at this cadence | Gear ratio | Development (per crank turn) | Gear inches |
|---|---|---|---|---|
| 11t | 53.98 km/h | 4.55:1 | 10.00 m | 125.3 in |
| 16t | 37.11 km/h | 3.13:1 | 6.87 m | 86.1 in |
| 21t | 28.27 km/h | 2.38:1 | 5.24 m | 65.6 in |
| 28t | 21.21 km/h | 1.79:1 | 3.93 m | 49.2 in |
Questions
What is a good gear ratio for climbing?
Something at or below 1:1, meaning the sprocket has at least as many teeth as the chainring. A 34 tooth chainring with a 34 tooth sprocket gives about 2.2 m of development, low enough for most sustained climbs. What counts as low enough depends on the gradient and the rider.
What is the difference between development and gear inches?
They express the same thing in different units. Development is metres travelled per pedal turn, which is directly meaningful. Gear inches is the wheel diameter multiplied by the ratio, a legacy from penny-farthings where the gear literally was the wheel size. Gear inches persists mainly in older and American sources.
Does wheel size change the gearing?
Yes, in direct proportion. A 650b wheel is smaller than a 700c, so the same gear ratio gives less development and a lower effective gear. This is why gravel bikes offered in both wheel sizes sometimes specify different gearing for each.
What cadence should I use?
Most trained cyclists sit between 80 and 100 rpm, and many riders naturally choose a lower cadence than is efficient. The calculator takes whatever you enter, so setting it to your own measured cadence gives speeds that reflect how you actually ride.
For frame sizing from your inseam, see the bike frame size calculator. For chain length, see the bike chain length calculator.