Free online gear ratio calculator. Enter driver and driven gear teeth to calculate gear ratio, output RPM, and output torque. Supports multi-stage gear trains. Pure frontend calculation, no data upload.
Zero Dependencies · Works OfflineEnter teeth for each stage. Total ratio is calculated automatically.
The gear ratio is the ratio of driven gear teeth to driver gear teeth:
Gear Ratio = Driven Teeth / Driver Teeth
Output RPM = Input RPM / Gear Ratio
Output Torque = Input Torque × Gear Ratio
Note: Actual output torque should account for transmission efficiency (typically 90%-98%). Values shown are theoretical.
The total ratio of a multi-stage gear train is the product of all stage ratios:
Total Ratio = Ratio₁ × Ratio₂ × ... × Ratioₙ
A gear ratio greater than 1 indicates a reduction drive — the output speed is lower than the input speed, but the output torque is higher. This is common in car low gears, power tools, and cranes where high torque is needed.
A gear ratio less than 1 indicates an overdrive — the output speed is higher than the input speed, but torque is reduced. This is used in wind turbines (slow rotor driving a fast generator) and vehicle highway gears.
Because each stage's output speed is the next stage's input. If stage 1 reduces speed by half (ratio 2) and stage 2 reduces by half again (ratio 2), the total effect is one-quarter (ratio 4). Stages are in series, so the total ratio is the product.
Spur gears: ~98%-99%. Helical gears: ~97%-98%. Bevel gears: ~95%-97%. Worm gears: ~50%-90% (depending on lead angle). Real-world calculations should multiply by the efficiency coefficient.