Mechanical

Gear Ratio Calculator

Calculate gear ratios, RPM output, and torque for gear trains.

Input Parameters

Calculate From

Driver Gear (Input) Teeth

Driven Gear (Output) Teeth

Input RPM (optional)

RPM

Input Torque (optional)

lb-ft

Gear Mesh Type

Results

Enter gear data and click Calculate

What is Gear Ratio?

Gear ratio is the relationship between the number of teeth on two meshing gears. It determines how rotational speed and torque are transferred between shafts.

A gear ratio greater than 1:1 provides speed reduction and torque multiplication - essential for matching motor output to load requirements in machinery, vehicles, and power transmission systems.

How to Use

Choose calculation mode (tooth count or RPM)
Enter driver (input) and driven (output) gear teeth
Optionally add input RPM and torque for full analysis
Select gear type (external reverses direction)
Click Calculate to see ratio and output values

FAQs

Gear ratio = Driven teeth ÷ Driver teeth. For example, if the input gear has 20 teeth and drives a gear with 60 teeth, the ratio is 60/20 = 3:1. This means the output shaft rotates once for every 3 rotations of the input shaft, with torque multiplied by approximately 3 (minus efficiency losses).

They're inversely related by the gear ratio. A 3:1 reduction means speed decreases to 1/3 while torque increases by 3x (minus losses). Power remains constant (P = Torque × Speed), so reducing speed proportionally increases torque. This is why gearboxes are used to match motor output to load requirements.

Efficiency represents power lost to friction and heat. Typical efficiency: spur/helical gears 95-98%, bevel gears 93-97%, worm gears 50-90% (highly ratio-dependent). A 4-stage gearbox at 95% per stage has overall efficiency of 0.95⁴ = 81%. Always account for efficiency in torque calculations.

A hunting tooth ratio occurs when the driver and driven tooth counts share no common factors (are coprime). For example, 21:60 instead of 20:60. This ensures each tooth on the small gear contacts every tooth on the large gear over time, distributing wear evenly and improving longevity.

Yes, the same ratio principles apply. For belt/chain drives, use pulley or sprocket teeth counts. If using smooth pulleys, the ratio equals the diameter ratio (large pulley diameter ÷ small pulley diameter). Chain drives behave like gears, while belt drives can slip under high load.

Limitations

• Assumes 95% efficiency - actual varies by gear type
• Single gear pair only - multi-stage requires multiplication
• Does not calculate gear dimensions or stress
• Worm gears have different efficiency characteristics
• Verify gears have matching pitch/module for mesh