Gear Ratio Calculator

A higher gear ratio (like 5:1 vs. 2:1) means more speed reduction and more torque multiplication. The driving gear must spin more times per output revolution. Higher ratios are used for starting from a stop (first gear in a car) or for high-torque, low-speed applications like winches and lifts.

Compound trains stack multiple gear pairs on shared shafts. Each pair's ratio multiplies with the others. Two stages of 3:1 and 4:1 give 12:1 overall. Three stages of 3:1 each give 27:1. This allows massive speed reductions in a compact package without requiring extremely large gears.

A gear reduction means the output is slower than the input (ratio > 1:1), delivering more torque. An overdrive means the output is faster than the input (ratio < 1:1), delivering less torque. Car transmissions use reductions in low gears for acceleration and overdrive in top gear for highway cruising.

Divide the motor RPM by your desired output RPM. To get 500 RPM from a 3,000 RPM motor: Ratio = 3,000 ÷ 500 = 6:1. Then select gear teeth: a 12-tooth driver and 72-tooth driven gear gives exactly 6:1.

No. Power (watts = torque × angular speed) is conserved through an ideal gear train. A 3:1 ratio triples torque but reduces speed by one-third, keeping power constant. Real gear trains lose 1-3% per stage to friction, so output power is slightly less than input power.

Divide your required output torque by the motor's available torque. If you need 50 Nm and your motor produces 5 Nm, you need a 10:1 gear ratio (plus margin for friction losses). Select a ratio of 11:1 to 12:1 to ensure adequate torque after efficiency losses.

Gear module (metric) or diametral pitch (imperial) defines the tooth size but does not change the ratio. A 20-tooth and 60-tooth gear give a 3:1 ratio regardless of tooth size. However, both gears in a pair must use the same module to mesh properly.

Spur gears: 94-98% per stage. Helical gears: 95-99%. Worm gears: 40-90% (depends on lead angle). Bevel gears: 93-97%. For multi-stage calculations, multiply the efficiencies: 3 stages at 97% = 0.97³ = 91.3% overall efficiency.

Not exactly. Standard gears come in specific tooth counts (typically 12 to 150+ teeth). The achievable ratios depend on available tooth count combinations. For precise non-standard ratios, use compound gear trains where multiplied ratios can approximate nearly any value.

Planetary (epicyclic) gear sets use a sun gear, ring gear, and planet gears orbiting between them. They achieve high reduction ratios in a compact, coaxial package. Ratios of 3:1 to 12:1 per stage are common. They are used in automatic transmissions, power tools, and robotic joints.

Bicycle gear ratio = front chainring teeth ÷ rear cassette teeth. A 50-tooth chainring with a 25-tooth rear cog gives a 2:1 ratio, meaning the rear wheel turns twice per pedal revolution. Multiplied by wheel circumference, this determines the distance traveled per pedal stroke (gear inches).