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Bicycle Gear Calculator

Calculate gear ratio, gear development, and speed at a cadence from chainring, cog, and wheel circumference.

Available

Inputs

Enter values

Live
Calculate speedFrom gear ratio and cadence

Gearing

Chainring and cog.

teeth

Front chainring on the crank.

teeth

Rear cog on the wheel.

m

Only fill in for custom circumference.

rpm

Optional – for speed.

Load example

For illustration only – your own calculation is what counts.

Explanation

How Bicycle Gear Calculator works

The bicycle gear calculator connects three metrics: the gear ratio from chainring and cog, development via wheel circumference, and resulting speed at a chosen cadence.

The Formulas

Gear RatioRatio = Chainring teeth ÷ Cog teeth

A 50-tooth chainring on a 12-tooth cog gives 50 ÷ 12 ≈ 4.17.

DevelopmentDevelopment = Ratio × Wheel Circumference

The distance traveled per crank revolution in meters.

SpeedSpeed = Development × Cadence

In km/h, when development is in meters and cadence in revolutions per minute.

Practice

Practical examples

For illustration only – your own calculation is what counts.

Biggest gear in sprint

A road bike with 50-tooth chainring and 12-tooth cog on 700×25c tires is pedaled at 90 rpm.

Result: The gear ratio is 4.17, development around 8.77 m, and speed at 90 rpm about 47.4 km/h.

Climbing gear

On a climb, the same crank shifts to 34-tooth chainring and 28-tooth cog (700×28c) at 80 rpm.

Result: The ratio drops to 1.21, development to around 2.59 m, and speed to about 12.5 km/h.

Notes

Common mistakes

  1. Swapping chainring and cog

    Those who swap the tooth counts get the reciprocal and thus a completely wrong gear.

    Front (crank) is the chainring, rear on the wheel is the cog.

  2. Choosing wrong wheel circumference

    Wider tires or a different wheel standard noticeably change rolling circumference.

    Choose the appropriate preset or enter your measured circumference.

FAQ

Frequently asked questions

What is the gear ratio?

The gear ratio is the number of chainring teeth divided by the number of cog teeth. It tells how many times the rear wheel turns per crank revolution. A larger ratio means a harder, faster gear.

What does development mean?

Development is the distance the bike travels with one full crank revolution. It results from the gear ratio times the rolling circumference of the tire and is stated in meters.

How does speed relate to cadence?

Speed is development times cadence. If you pedal the same gear faster, speed increases proportionally to cadence. That's why a steady, smooth cadence of about 80 to 100 rpm pays off.

Where does wheel circumference come from?

Rolling circumference depends on rim and tire width. The presets use ETRTO reference values (e.g., 2.105 m for 700×25c). For maximum accuracy, you can enter your measured rolling circumference.

How do I measure rolling circumference myself?

Mark valve and ground, roll the loaded wheel exactly one revolution, and measure the distance. This is more accurate than any table because tire pressure and rider weight are factored in.

What cadence makes sense?

Most cyclists ride most economically in the range of 80 to 100 rpm. Very low cadences stress muscles and joints more, very high ones cost unnecessary energy.

Limits

Limitations

  • Speed is a theoretical value without wind, gradient, and drivetrain losses.
  • Tire pressure, wear, and rider weight change actual rolling circumference.

Sources

Sources and references

  • ETRTO – Reifen-Abrollumfänge (Standards Manual)European Tyre and Rim Technical Organisation

    Defines standardized rolling circumferences of common wheel/tire combinations.

    Retrieved: 09/23/2026 · Verified on: 09/23/2026
  • Übersetzung, Entfaltung und Trittfrequenz im RadsportFahrradmechanik (Grundlagen der Kraftübertragung)

    Describes the relationship of tooth counts, rolling circumference, and speed.

    Retrieved: 09/23/2026 · Verified on: 09/23/2026