Calculators
Gear ratio calculator
Every chainring against every cog: ratio, gear inches, development, gain ratio and road speed. Enter teeth counts directly — anything the presets miss can be typed in.
Speed range per gearbars span 60–110 rpm, the mark is your cadence
Overlapping bars mean two gears do the same job. Gaps mean a cadence you cannot hold at that speed in any gear.
Step between gearsshifting up through the cassette
The jump from each gear to the next, as a percentage. Under about 10% feels smooth; much over 15% and you will notice the cadence drop on every shift.
Every combination
| Front | Rear | Ratio | Gear inches | Development | Gain ratio | Speed |
|---|
How it is worked out
Nothing here is proprietary — these are the standard definitions, and the gain ratio is Sheldon Brown's. Every figure in the table above comes from one of them.
1 · Wheel diameter and circumference
The tyre sits on top of the rim on both sides, so it adds twice its width to the diameter.
BSD is the rim's bead seat diameter (622 mm for 700c), w the tyre width. This is the usual approximation — a real tyre is not perfectly round and squashes under load, so a rollout measurement will differ by a percent or so.
2 · Gear ratio
How many turns the wheel makes for one turn of the cranks.
Tf chainring teeth, Tr cog teeth.
3 · Gear inches
The old penny-farthing measure: the diameter of the wheel you would need to go this far per pedal stroke without gears. Handy because everyone quotes it.
Divide by 25.4 to turn millimetres into inches.
4 · Development
How far you actually travel for one full turn of the cranks.
The most physical of the four — metres of road per pedal revolution.
5 · Gain ratio
Sheldon Brown's measure, and the only one that accounts for crank length. It compares how far the wheel travels to how far your foot travels, so it is a pure number: a gain ratio of 5 means the bike moves five times as far as your foot does around the circle.
L is crank length. Two riders on the same gear inches but different cranks are not pushing the same gear, which is the whole point of this one.
6 · Speed
Development times how many times a minute you turn the cranks.
n is cadence in rpm, D in metres, giving km/h. Assumes no freewheeling, no wheel slip and a tyre that measures what it says.