Bike Cadence and Speed Calculator

Your speed on a bike comes from three things: how fast you pedal, what gear you are in, and how big your wheels are. Cadence is how fast you pedal, measured in revolutions per minute (RPM). The gear is set by the ratio of the front chainring teeth to the rear cog teeth. Each pedal stroke turns the rear wheel by that ratio, and the wheel rolls forward by its circumference. Multiply it through and you have speed.

The gear ratio matters more than people expect. A 50-tooth chainring paired with a 14-tooth cog gives a ratio of about 3.57, so one turn of the pedals spins the wheel three and a half times. Drop to an 11-tooth cog and the same cadence carries you noticeably faster, which is why sprinters shift into the small cogs. The flip side is effort: a bigger gear is harder to push, so on a climb you spin a smaller ratio to keep your legs turning.

Two numbers describe a gear without mentioning speed. Development, or rollout, is how far the bike travels per pedal revolution, in meters. Gear inches is an older measure, the equivalent wheel diameter if you had no gears at all, and it lets riders compare setups across wheel sizes. Both appear in the result.

Most road cyclists hold a cadence of 80 to 100 RPM on the flat. Spinning faster in an easier gear is usually gentler on the knees than grinding a big gear slowly. One thing to keep in mind: this is steady-state, no-slip speed. Real road speed sits a touch lower once you account for wind, drivetrain friction, and the moments you stop pedaling to coast.

A worked example. Take a 50-tooth chainring, a 14-tooth cog, 700c wheels with 25 mm tires, and 90 RPM.

• Gear ratio: 50 ÷ 14 = 3.57
• Development: 3.57 × 2.105 m = 7.52 m per pedal stroke
• Speed: 7.52 × 90 × 60 ÷ 1,000 = 40.6 km/h, or 25.2 mph
• Gear inches: 3.57 × 26.38 in = 94.2

Gear inches is the odd one out there, and it is worth a sentence. It comes from the penny-farthing era, when the only way to change gearing was to change the size of the front wheel you sat on. A 94-inch gear means this bike travels as far per pedal stroke as a direct-drive bicycle with a 94-inch wheel would, which is a wheel taller than most riders. It survives because it collapses chainring, cog and wheel size into one number you can compare across any two bikes.

Rough ranges to compare against: under 30 gear inches is a loaded-touring climbing gear, 70 to 90 is flat-road cruising, and anything over 100 is a descent or a sprint. Most riders spin out somewhere around 120.

Wheel circumference is not the number printed on the tire. A 700×25c tire rolls about 2,105 mm per turn, not 700 mm, and a 29-inch wheel rolls about 2,300 mm rather than 29 inches. The presets above carry the rolling circumference for each size so there is nothing to convert. If you want your own figure, mark the tire, roll the bike one full turn on the ground with your weight on it, and measure the distance between marks. That accounts for tire pressure and squash, which published charts cannot.