Cycling Speed Calculator
Enter your cadence, the teeth on your chainring and rear cog, and your wheel or tyre size. The calculator gives your speed in km/h and mph, the gear ratio, gear inches and the distance you roll per pedal revolution. Results are estimates, because real rollout changes slightly with tyre pressure and load. It also answers how fast you go in a given gear, for example at 80 rpm with a 39 tooth chainring and a 25 tooth cog.
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Formula
gear ratio = chainring teeth / cog teethdevelopment (m) = gear ratio x wheel circumference (m)speed (km/h) = cadence (rpm) x development (m) x 60 / 1000speed (mph) = speed (km/h) / 1.609344gear inches = gear ratio x wheel diameter (in), withdiameter = circumference / pi / 25.4
Wheel presets use typical rollout values (for example 2105 mm for a 700 x 25c tyre). The speed is an estimate: it assumes constant cadence and no coasting.
Worked example
50 teeth chainring, 17 teeth cog, 700 x 25c wheel (2105 mm), cadence 90 rpm:
- Gear ratio: 50 / 17 = 2.941
- Development: 2.941 x 2.105 m = 6.19 m per pedal turn
- Speed: 90 x 6.19118 x 60 / 1000 = 33.43 km/h, which is 20.77 mph
- Gear inches: 2.941 x 26.38 in = 77.6
When to use it
Use it to compare gear choices before buying a cassette or chainring, to choose gears for a hilly route, or to check what speed a cadence target gives you. Fixed gear and single speed riders use gear inches and development all the time.
Typical values (rules of thumb)
- Comfortable cadence for most road riders is roughly 80 to 100 rpm.
- Gear inches below about 40 are very easy climbing gears, 60 to 80 suit rolling terrain and above 100 are fast flat or downhill gears.
Common mistakes
- Using nominal tyre width instead of a rollout. A 700x25c tyre rolls about 2.1 m; the true figure depends on the tyre and pressure.
- Mixing up teeth counts. The chainring is the front ring and the cog is the rear sprocket.
- Expecting the speed to match your head unit exactly while coasting, braking or in wind.
How it differs from nearby tools
The speed converter changes units only. The cycling power to weight calculator and the cycling calories calculator work from watts, not gearing. The triathlon time calculator handles the full race.
Frequently asked questions
How do I calculate bike speed from cadence and gearing?
Divide the chainring teeth by the cog teeth, multiply by the wheel circumference to get the distance per pedal turn, then multiply by cadence. For 50/17 on a 2105 mm wheel at 90 rpm: 2.941 x 2.105 m = 6.19 m per turn, and 90 x 6.19 m x 60 / 1000 = 33.43 km/h (20.77 mph).
What are gear inches?
Gear inches are the diameter of a direct-drive wheel that would roll the same distance per pedal turn: gear ratio x wheel diameter in inches. A 50/17 gear on a 2105 mm wheel (diameter 26.4 in) gives 2.941 x 26.4 = 77.6 gear inches.
What is development in metres?
Development, also called rollout, is how far the bike travels for one full pedal turn: gear ratio x wheel circumference. A 34/28 gear on a 2000 mm wheel travels 1.214 x 2.000 m = 2.43 m per turn.
What wheel circumference should I use?
The presets are typical rollout values for common tyres, for example 2105 mm for a 700 x 25c. Your own figure can differ by a few millimetres with tyre brand, pressure and rider weight. For the most accurate result, measure the distance of one wheel revolution with you on the bike and enter it as a custom circumference.
Is the speed shown exact?
It is an estimate of the speed your gearing and cadence imply with no slip or coasting. Wind, hills and stopping change your real average speed, and cadence usually varies along a ride.
How fast do you go at 80 rpm with a 39 by 25 gear?
With a 700x25c wheel (2105 mm), the gear ratio is 39 / 25 = 1.56, so each pedal turn rolls 3.28 m. At 80 rpm that is 15.76 km/h, or 9.79 mph.
How do you calculate gear ratio on a bike?
Divide the teeth on the chainring by the teeth on the rear cog. A 50 tooth chainring with a 17 tooth cog is 50 / 17 = 2.94, so the wheel turns 2.94 times for each pedal revolution.
What cadence do I need for 30 km/h in a 50x17 gear?
With a 700x25c wheel one pedal turn rolls 6.19 m, so cadence = 30,000 / 60 / 6.19 = about 81 rpm.