Speed follows your chosen units. Tire circumferences and crank lengths stay in millimeters to match component markings; gear inches remain inches by definition.
How to use this bicycle gear calculator
Start with your actual chainring and sprocket tooth counts. Use a reference wheel circumference or measure your own. Examples describe possible ratios, not compatible parts.
How the calculation works
Gear ratio = front chainring teeth ÷ rear sprocket teeth. One crank revolution turns the wheel that many times. This convention is the inverse of an input-to-output reduction ratio often used for mechanical gears.
Development = wheel circumference in meters × gear ratio. Gear inches = wheel circumference in millimeters ÷ π ÷ 25.4 × gear ratio. Gain ratio = wheel radius ÷ crank length × gear ratio, using the same length unit for both.
Speed in km/h = development × cadence × 60 ÷ 1000. Divide by 1.609344 for mph. To reverse it, cadence = speed in km/h ÷ (development × 0.06). Cadence mode checks every entered gear against your preferred range.
Overall range = highest ratio ÷ lowest ratio × 100%. An 11–50 single-ring cassette spans 454.55%. That is a 354.55% increase from its lowest to highest ratio, a different percentage. Sorted steps in the chart are relative increases from the preceding ratio, not a suggested shifting sequence.
For a gearing change, lowest-gear change = (proposed lowest development ÷ current lowest development − 1) × 100%. A negative result travels less distance per crank turn. Top-gear change uses the same comparison. Each setup keeps its own wheel circumference and crank length.
Worked example
With a 50-tooth ring, 20-tooth cog and 2,100 mm measured wheel circumference, the ratio is 2.5, development is 5.25 m, and 90 rpm gives 28.35 km/h (17.62 mph). At 170 mm crank length, gain ratio is about 4.915.
Limits and assumptions
For external chainring/cassette gearing or a single-speed direct chain drive. Includes all mathematical combinations, even extreme small/small and big/big chainlines. It does not certify derailleur capacity, chain length, hub/freehub or frame compatibility. Internal hubs, gearboxes, belt-drive ratios, traction, wind, slope and rider power are outside this model.
Frequently asked questions
Which cassette teeth should I enter?
Use the full tooth sequence printed in the manufacturer’s specification or count each sprocket. 11–32 alone gives only the endpoints and cannot describe the steps between gears. A single rear tooth count works for a single-speed bike.
Is 700C a 700 mm wheel diameter?
No. It is a tire-size family; actual outside size and loaded rollout depend on the tire. Choose a stated reference circumference or measure one loaded revolution. Do not enter a bare rim diameter as wheel circumference.
Can I compare road, gravel and folding bikes?
Yes, when they use the supported chain drive. Give each setup its own wheel circumference. Gear inches, development and gain ratio let you compare beyond the tooth ratio alone.
Can I find the right cadence for a target speed?
Choose the speed and cadence-range mode. Each combination shows required rpm and whether it fits your chosen range. If none match, the page says so and still shows the full chart.
Does a lower gear guarantee I can climb a hill?
No. It changes the mechanical relationship between pedaling and wheel movement. Rider power, load, traction and gradient still matter.