Tools you might need next
Calculate bicycle gear ratios, gear inches, and development for any chainring and cassette cog combination on your bike.
Find the correct bicycle frame size from inseam, height, and riding style for road, mountain, hybrid, and gravel bicycles.
Calculate bicycle spoke length from hub flange diameter, rim ERD, lacing pattern, and number of crosses for wheel building.
Each crank turn moves the bike forward by gear ratio times wheel circumference.
speed = cadence (rpm) × development × 60 / unit conversionHigher cadence or harder gear increases speed linearly if power can be maintained.
Use measured rollout or labeled tire size. Small circumference errors matter at high cadence.
Updated: July 2026
Map 90 RPM on a flat gear to expected outdoor mph on your road bike.
Find cadence needed to hold 25 mph in your big ring on a flat course.
Compare virtual speed display to calculated speed for a given gear on a wheel-on trainer.
Speed depends on the full ratio. A 50T ring with 28T cog is much slower than with 11T at the same cadence.
Very high or low gears may be unsustainable at target cadence. Check power and knee comfort.
See how fast you will go at a given cadence in any gear. Enter RPM, chainring and cog teeth, and wheel size to get speed in mph or km/h.