Gear Ratio Calculator & Speed Chart
Gear ratio = Driven Teeth (N2) ÷ Driver Teeth (N1). Output Speed (RPM2) = Driver Speed (RPM1) ÷ Gear Ratio.
| Gear Ratio | Sample Teeth Mesh (Driven : Driver) | Speed Multiplier (RPM2/RPM1) | Ideal Torque Multiplication |
|---|---|---|---|
| 1:1 Direct | 15 : 15 | 1.00× Speed | 100% Torque |
| 2:1 Reduction | 30 : 15 | 0.50× Speed | 200% Torque |
| 3:1 Reduction | 45 : 15 | 0.333× Speed | 300% Torque |
| 4:1 Reduction | 60 : 15 | 0.25× Speed | 400% Torque |
| 5:1 Reduction | 75 : 15 | 0.20× Speed | 500% Torque |
| 10:1 Reduction | 100 : 10 | 0.10× Speed | 1,000% Torque |
| 20:1 Compound | 200 : 10 | 0.05× Speed | 2,000% Torque |
| 50:1 Worm Gear | 50 : 1 | 0.02× Speed | 5,000% Torque |
Technical standards per KHK Gear Technical Reference, AGMA Standards, and Wikipedia Gear Ratio.
Calculation Results
Calculated estimations for your inputs:
RPM vs Speed Reference Table
| Engine RPM | Speed |
|---|
Sources & Governing Codes
- Wikipedia Gear Mechanics & Pitch Diameter: Wikipedia Gear Mechanics & Pitch Diameter View Standard
- Wikipedia Gear Train Velocity Ratios: Wikipedia Gear Train Velocity Ratios View Standard
Frequently Asked Questions (FAQ)
How is gear ratio calculated?
Gear ratio is calculated by dividing the number of teeth on the driven gear by the number of teeth on the drive (pinion) gear: Gear Ratio = Driven Teeth / Drive Teeth.
What is a speed reduction ratio?
A speed reduction ratio multiplies output torque while reducing speed. A 3:1 gear ratio means the input shaft turns three times for every single rotation of the output shaft.
How does gear ratio affect torque?
Output torque is directly proportional to gear ratio (ignoring friction losses). A 4:1 gear ratio multiplies input torque by 4, allowing smaller motors to turn heavy loads.
What is gear backlash?
Backlash is the clearance gap between mating gear teeth, designed to prevent binding, allow lubrication, and account for thermal expansion under load.
What is a pinion gear?
The pinion is the smaller gear in a mating pair, usually mounted on the drive shaft (input) to initiate rotational speed transfers.
How do you calculate compound gear ratio?
For compound gear trains, calculate the individual ratio of each gear pair, then multiply them together: Total Ratio = Ratio 1 × Ratio 2 × Ratio 3.
How does tire diameter affect final drive speed?
In automotive drivetrains, overall speed depends on transmission ratio, final drive ratio, and tire diameter. Larger tires cover more ground per rotation, increasing top speed but reducing acceleration torque.
What is the gear pitch circle?
The pitch circle is the imaginary circle where the mating teeth of two gears contact, used to calculate nominal diameters and velocity ratios.
Why do gears have helical cut teeth?
Helical gears feature angled teeth that engage gradually, reducing noise and vibrations compared to straight-cut spur gears, making them standard in automotive gearboxes.
How do you calculate speed from gear ratio and RPM?
Output RPM is equal to Input RPM divided by the Gear Ratio. Vehicle speed is then calculated using output RPM, final drive, and tire circumference.
How is gear ratio calculated from tooth counts?
Gear Ratio = Driven Gear Teeth (Ring/Output) ÷ Driving Gear Teeth (Pinion/Input).
How does gear ratio affect output torque and speed?
A higher gear ratio (e.g., 4.10:1 vs 3.55:1) increases output torque and acceleration while proportionally reducing top speed and output RPM.
What is the difference between a speed reducer and an overdrive gear train?
A speed reducer has a ratio > 1.0 (input spins faster than output, increasing torque). An overdrive ratio is < 1.0 (output spins faster than input).
How do you calculate overall gear ratio in a compound gear train?
Overall Gear Ratio = Ratio 1 × Ratio 2 × Ratio 3... (multiply the individual gear pair ratios sequentially).
How does tire diameter change affect effective final drive ratio?
Installing taller tires decreases effective axle gear ratio, reducing engine RPM at highway speeds but decreasing low-end towing torque.
What is pitch diameter in gear geometry calculations?
Pitch diameter is the imaginary operating pitch circle diameter where meshing gear teeth transfer pure rolling motion without slipping.
How do idler gears affect overall gear ratio and direction of rotation?
Idler gears placed between driving and driven gears reverse direction of rotation but do NOT change the overall velocity ratio.
What is gear module or diametral pitch?
Diametral pitch (US) is the number of teeth per inch of pitch diameter. Module (Metric) is pitch diameter in mm divided by number of teeth.
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