🎥 Video — Gear Ratio Calculator & Complete Guide — Formula, Types, and How Gears Work
Engineering notes for gear ratio
A gear ratio is not just a speed change. It is a torque, speed, backlash, efficiency, and packaging decision.
Robbie Dickson-style engineering note: do the simple calculation first, then check the ugly real-world parts: mounting stiffness, friction, duty cycle, tolerances, and what happens when the mechanism is at its worst angle.
Core formula
Gear ratio = driven gear teeth / drive gear teeth. Output speed = input speed / ratio. Output torque = input torque x ratio x efficiency.
Worked calculation example
Assume a 3,000 rpm motor drives a 60 tooth gear from a 12 tooth pinion. The ratio is 5:1. Ignoring losses the output speed is 600 rpm; at 85 percent efficiency the useful output torque is about 4.25 times the motor torque.
Selection table
| Case | Engineering effect | Practical use |
|---|---|---|
| Low ratio | Fast output, modest torque gain | Light loads, short duty cycle motion |
| Medium ratio | Balanced speed and torque | General automation, positioning, linkages |
| High ratio | Slow output, high torque gain | Heavy loads, holding force, controlled motion |
Practical checks before choosing parts
- Confirm the load path and the worst-case position, not only the average position.
- Use consistent units through the full calculation and write down every assumption.
- Add a safety factor for friction, wear, impact, unknown loading, and mounting flex.
- Check duty cycle, current draw, heat, and bracket strength before treating the result as final.
- Bench test the mechanism when the cost of being wrong is higher than the cost of a quick prototype.
Useful FIRGELLI resources to cross-check
- Free Differential Gear Ratio Calculator — RPM and Speed | FIRGELLI Eng - Shared topic terms: firgelli, gear, ratio
- Gear Ratio Calculator Speed Torque Teeth - Shared topic terms: gear, ratio
- Gear Ratio Converter - Shared topic terms: gear, ratio
- Gear Ratio Speed Calculator Final Drive - Shared topic terms: gear, ratio
- Gear Tooth Strength Calculator Lewis Formula - Shared topic terms: formula, gear
- Worm Gear Calculator Ratio Efficiency - Shared topic terms: gear, ratio
FAQ
Does a higher gear ratio always mean more force?
It increases torque, but friction, gearbox efficiency, backlash, and shaft strength decide how much useful force reaches the load.
What efficiency should I assume?
For a first calculation, use 80 to 90 percent for a decent gear train, then verify with measured current, temperature, and load testing.
What is the common sizing mistake?
Sizing only from ideal torque. In practice, add a safety factor and check duty cycle, stall current, mounting stiffness, and backlash.
