Transmission Calculator (Gear Ratio)

Transmission Gear Ratio Relationships

A gear transmission trades speed for torque according to its gear ratio. Output speed is N₂ = N₁ / ratio, while output torque is T₂ = T₁ × ratio × η, where N₁ and T₁ are input speed and torque, and η is the mechanical efficiency accounting for friction losses in the gears and bearings.

A gear ratio greater than 1 (a reduction) lowers output speed but increases output torque; a ratio less than 1 (an overdrive) does the opposite. Efficiency losses mean the output power is always slightly less than the input power, with the difference dissipated mostly as heat.