This bike cadence and speed calculator turns pedaling rhythm into road speed: speed = cadence × (chainring ÷ cog) × wheel circumference — with gear inches and meters of development for every gear you own.

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Pedals, Teeth, and One Circumference

A bicycle’s speed is fully determined by three multiplications a child could audit: your cadence (crank rpm) turns the rear wheel faster by the gear ratio (chainring teeth ÷ cog teeth), and each wheel revolution rolls out exactly one tire circumference of road. The defaults describe club-riding reality — 90 rpm in a 50×15 (ratio 3.33) on 700×25c tires gives 37.9 km/h, with 7.02 m of development per pedal revolution and about 88 gear inches. The same arithmetic explains the whole cassette’s purpose: at a fixed comfortable cadence of 90, a modern 52/36 × 11–28 setup spans from ~17 km/h (36×28, climbing gear) to ~64 km/h (52×11, descent sprint gear) — the rider keeps the rhythm, the teeth do the translating. It also explains the fixed-gear world’s obsession with gear inches and why two riders at identical speed can be pedaling 20 rpm apart: speed is a product, and cadence is only one of its factors.

Accuracy lives in the circumference: the preset values are ETRTO-standard approximations, but real rollout varies a few millimeters with tire pressure, rider weight (the tire squishes into an effectively smaller circle) and wear — measured rollouts (mark the floor, roll one full wheel turn under load, measure) tighten the estimate to under 1%, which is why bike computers ask for the number. The second honesty note: this is drivetrain math, not a promise — wind, gradient and drafting decide what a given speed COSTS, while the calculator only states what a gear and cadence PRODUCE on a free-rolling wheel. Used in reverse it’s the gearing planner’s tool: pick a target speed at your sustainable cadence (climbs at 75–85 rpm, cruising 85–95, sprint finishes 110+) and the required ratio falls out, telling you whether your cassette owns that gear at all.

Worked Examples (Verified)

  • Defaults: 90 rpm, 50×15, 700×25c → 37.9 km/h, development 7.02 m, ≈88 gear inches.
  • Climbing gear: 80 rpm in 34×28 (ratio 1.21) → 12.3 km/h — steep-ramp speed at a sustainable spin.
  • Sprint gear: 110 rpm in 52×11 (ratio 4.73) → 65.6 km/h.
  • Commuter cruise: 75 rpm in 42×18 on 700×32c → 22.4 km/h.

Bike Gearing Discipline

  • Measure rollout for precision work (track, TT pacing): pressure and load move circumference by up to 1%, and 1% of 40 km/h is visible.
  • Development is the portable gear unit across wheel sizes — compare bikes by meters developed, not by teeth alone (a 26″ MTB and a 700c road bike with equal teeth are NOT equally geared).
  • Cadence choice is physiology, not math: 85–95 rpm cruising spares knees and glycogen versus grinding 60 rpm at the same speed in a bigger gear.
  • Cross-chaining doesn’t change the ratio, only the wear and noise — the calculator’s answer stands even when the chainline complains.
  • E-bikes obey the same drivetrain arithmetic; the motor changes who pays for the speed, not the speed a gear and cadence produce.

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Frequently Asked Questions

How do you calculate bike speed from cadence and gearing?

Speed = cadence (rpm) × gear ratio (chainring ÷ cog) × tire circumference, converted to per-hour. At 90 rpm in 50×15 on a 700×25c tire (2.105 m): 90 × 3.33 × 2.105 = 632 m/min = 37.9 km/h. This calculator does the whole chain and also reports development (metres travelled per pedal revolution) and gear inches, the two traditional gear-size units.

What are gear inches and meters of development?

Two dialects for “how big is this gear.” Development is the distance the bike travels per full pedal revolution (ratio × wheel circumference in metres — 7.02 m at the defaults). Gear inches is the same idea in Victorian units: development ÷ π, expressed in inches — the diameter of the penny-farthing wheel that gear mimics (88 inches at the defaults). Development wins for comparisons across wheel sizes because teeth alone mislead: equal gears on different wheels are different gears, equal developments are equal.

What cadence should I ride at?

For most riders, 85–95 rpm for steady cruising is the efficient, knee-friendly band the sport converged on; climbing drops to 75–85 under load, time trials sit at 90–100, and sprint finishes exceed 110. Beginners typically self-select 60–70 rpm and gain free comfort (and late-ride durability) by gearing DOWN to spin faster at the same speed — the calculator shows exactly which cog restores your target cadence when speed is fixed: ratio = speed ÷ (cadence × circumference). Grinding big gears at low cadence is a knee-injury mechanism, not a strength program.

How much speed do I gain from one cog smaller?

Proportionally to the ratio change: dropping from a 16t to a 15t cog at the same chainring multiplies speed by 16/15 ≈ +6.7% (e.g., 35.5 → 37.9 km/h at 90 rpm on a 50t ring). Cassette steps are designed around that percentage logic — tight 1-tooth jumps at the small end (where each tooth is a big percentage), wider jumps at the climbing end. This is also why “one gear harder” feels trivial at 25 km/h and significant at 40: the percentage is constant, the watts behind it are not.

Does tire size change my speed?

Yes, arithmetically: the circumference is a direct factor — a 700×32c (2.136 m) rolls 1.5% further per revolution than a 700×23c (2.096 m) at identical gearing and cadence. It also changes effective gearing the same 1.5%. Real rollouts vary slightly with pressure and rider weight (the loaded tire’s effective radius shrinks), which is why careful riders calibrate a bike computer with a measured rollout rather than the printed chart — the presets here are the standard ETRTO-derived values those charts use.

Why does my bike computer disagree with this calculator?

Usually the circumference setting: if the computer’s stored wheel size differs from your actual tire (or was left on a default from another wheelset), every speed and distance it shows is off by the ratio of the two circumferences. GPS computers avoid the issue by measuring position — and disagree instead in tunnels and dense tree cover. Check: ride a measured kilometer in one gear at steady cadence against this calculator’s prediction; agreement within ~1% validates both, and a consistent percentage gap fingerprints the circumference entry as the culprit.

What gear do I need to climb at 10 km/h?

Work backward from your sustainable climbing cadence: at 80 rpm on 700×25c, 10 km/h requires ratio = (10,000/60) ÷ (80 × 2.105) ≈ 0.99 — essentially a 1:1 gear (34×34, or 36×36). On steeper ramps at 8 km/h the requirement falls to ~0.79 (34×42 territory), which is why gravel and MTB cassettes now ship 42–52t cogs while road compacts stop at 34. Enter your cadence and candidate gears into this calculator and read the speeds directly — the climbing gear you need is the one whose row in that table matches your hill speed.

Is this bike cadence and speed calculator free?

Yes — free, instant, no sign-up. Enter cadence, chainring, cog and tire for your speed, gear ratio, development and gear inches.