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About this tool
Turn cadence, chainring, cog and wheel size into road speed, gear inches, gain ratio and metres of development.
Cadence, gearing and speed are locked together by one relationship: one turn of the cranks moves the bike forward by (chainring ÷ cog) × wheel circumference, so speed in km/h is simply that development in metres times cadence times 60, divided by 1000. This calculator applies it and also reports gear inches (ratio × wheel diameter in inches) and Sheldon Brown's gain ratio (wheel radius ÷ crank length × ratio), which is the only common measure that accounts for crank length. Wheel circumferences come from the standard rollout tables used by cycle computers, and you can enter your own measured figure.
Open Cycling Cadence Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Uses measured wheel rollout rather than a nominal wheel size.
Ratio, gear inches and gain ratio, so you can compare bikes any way you like.
See the speed for the same gear from 60 to 120 rpm at a glance.
About 33.4 km/h on a 700x25c wheel. The gear ratio is 2.94, each crank turn covers 6.19 m of development, and 90 turns a minute works out to 557 m per minute.
Most trained road cyclists self-select 80 to 100 rpm on flat ground, and drop to 60-75 rpm on steep climbs where gearing runs out. Below about 60 rpm the same power requires much higher pedal force, which loads the knees; above 110 rpm efficiency starts falling for most riders.
Gear inches multiplies the gear ratio by wheel diameter in inches and ignores crank length entirely. Gain ratio divides wheel radius by crank length first, so it reflects the actual mechanical advantage — two bikes at 78 gear inches with 165 mm and 175 mm cranks are genuinely different gears, and only gain ratio shows it.
Sit on the bike at your normal tyre pressure, mark the tyre and the floor at the same point, roll forward exactly one wheel revolution, and measure between the marks. That rollout is a few millimetres shorter than the unloaded figure and is what your cycle computer needs for accurate speed and distance.
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