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Gear Ratio Calculator

Use Bicycle mode for chainring, rear cog, cadence, gear inches, development, and speed. Switch to Simple gear pair mode for one driver/driven pair to estimate output RPM and ideal torque multiplier.

For bicycles, front teeth mean the chainring and rear teeth mean the rear cog or sprocket. All calculations run in your browser; share URLs include only your input values and selected options.

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Calculate bicycle gearing or one gear pair

Choose the calculation mode, then enter teeth counts and the active wheel size source. Inactive wheel fields are ignored.

Enter a bicycle setup to calculate speed, gear inches, and development.

Formulas

Bicycle mode: gear ratio = front teeth ÷ rear teeth; development (m/rev) = wheel circumference (m) × gear ratio; speed (km/h) = development (m/rev) × cadence (rpm) × 60 ÷ 1000. mph is converted from km/h using 0.621371. Gear inches = wheel diameter in inches × gear ratio.

Simple gear pair mode: speed ratio = driver teeth ÷ driven teeth; output RPM = input RPM × speed ratio; torque multiplier = driven teeth ÷ driver teeth. Output torque applies the efficiency value you enter.

Limits

Torque output is an ideal estimate from tooth counts and the efficiency value you enter. It does not check gear strength, shaft loads, tooth profile, lubrication, wear, or safety margins.

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Torque, RPM & Power Calculator connects shaft torque, speed, kW, hp, and PS. Speed Distance Time Calculator helps convert travel speed and time. Work Energy Power Calculator covers ideal mechanical work and power.

FAQ

What is a bike gear ratio?

A bike gear ratio is front chainring teeth divided by rear cog teeth. A higher ratio moves farther per pedal revolution, while a lower ratio is easier to turn.

How do I calculate bike speed from cadence?

Bike speed in km/h equals development (m/rev) × cadence (rpm) × 60 ÷ 1000. The mph value is converted from km/h.

What are gear inches?

Gear inches equal wheel diameter in inches times the bicycle gear ratio. They are a traditional way to compare bicycle gearing.

What is the difference between speed ratio and torque multiplier?

For one external gear pair, speed ratio is driver teeth divided by driven teeth. Torque multiplier is the reciprocal, driven teeth divided by driver teeth, before efficiency losses.

Can I use this for gear design safety?

No. Torque output is an ideal estimate from tooth counts and entered efficiency only. It does not check gear strength, shaft loads, tooth profile, lubrication, wear, or safety margins.