Gear Ratio Calculator - Free Online Gear Train Analysis Tool
Gear Ratio Calculator
Calculate gear ratios, speed reduction/multiplication, torque relationships, and design multi-stage gear trains for mechanical systems.
Simple Gear Pair Calculator
Input Gear (Driver)
Output Gear (Driven)
Common Gear Ratio Applications
Speed Reduction
- • Winch: 20:1 to 100:1
- • Conveyor: 10:1 to 50:1
- • Mixer: 5:1 to 30:1
Automotive
- • 1st gear: 3.5:1
- • Final drive: 3:1 to 4:1
- • Overdrive: 0.7:1
Industrial
- • Pump drive: 2:1 to 5:1
- • Fan drive: 1.5:1 to 3:1
- • Mill drive: 10:1 to 100:1
How to use this calculator
⚙️ How to Use This Calculator
- Select the type of gear system: simple pair, compound train, or planetary
- Enter the number of teeth for each gear
- Input the driving gear speed and torque (if known)
- Click calculate to see gear ratio and performance parameters
- View the visual representation and detailed calculations
📐 Gear Ratio Formulas
Simple Gear Pair
Gear Ratio = N_driven / N_driver
Output Speed = Input Speed × (N_driver / N_driven)
Output Torque = Input Torque × (N_driven / N_driver) × η
Compound Gear Train
Total Ratio = Π(N_driven / N_driver) for all stages
Direction = (-1)^n where n = number of gear meshes
Planetary Gear (Ring Fixed)
Ratio = 1 + (N_ring / N_sun)
N_ring = N_sun + 2 × N_planet
🌟 Practical Examples
20-tooth pinion driving 80-tooth gear = 4:1 reduction
1800 RPM motor → 450 RPM output, 4× torque increase
1st gear: 14:43 × 17:37 = 3.66:1 total ratio
High torque for starting from rest
Sun: 13 teeth, Ring: 51 teeth = 4.92:1 ratio
Compact high-torque design
💡 Design Tips
- • Use prime numbers of teeth to distribute wear evenly
- • Minimum 12-17 teeth to avoid undercutting (depends on pressure angle)
- • Hunting tooth ratios (non-integer) improve gear life
- • Consider 20° or 25° pressure angle for strength
- • Account for efficiency: ~98% per mesh for precision gears
- • Planetary gears offer high ratios in compact space
⚠️ Common Mistakes to Avoid
- • Not checking for interference in planetary designs
- • Ignoring backlash requirements for reversing loads
- • Using too few teeth (causes undercutting)
- • Forgetting efficiency losses in multi-stage drives
- • Not considering tooth strength for high torque applications
- • Mismatching module/pitch between mating gears
About this calculator
Calculate gear ratios, speed ratios, torque multiplication, and mechanical advantage. Design gear trains with multiple stages.
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