Physics

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Gear Ratio Calculator.

Calculate ideal gear ratio, output speed, and torque.

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01

Set your values

Results update as you type.

Gear ratio: 3

Gear ratio

0.000000
Output speed: 600 rpm

Output speed

0.000000rpm
Output torque: 30 N·m

Output torque

0.000000N·m

Results update automatically as you type.

Use Cases

Designing gear trains for machinery

Determine the appropriate gear ratio to achieve desired output speed and torque for mechanical systems.

Example: A conveyor belt needs to run at 100 rpm with a motor spinning at 1500 rpm, so a gear ratio of 15:1 is required.

Optimizing vehicle performance

Select gear ratios for transmissions or differentials to balance acceleration and top speed.

Example: Changing the final drive ratio from 3.5 to 4.1 increases torque at the wheels but reduces top speed.

Frequently Asked Questions

How do I calculate the gear ratio?
Divide the number of teeth on the driven gear by the number of teeth on the driving gear. For example, if the driven gear has 40 teeth and the driving gear has 10 teeth, the gear ratio is 4:1.
What is the output speed formula?
Output speed = Input speed / Gear ratio. If the input speed is 1000 rpm and the gear ratio is 4:1, the output speed is 250 rpm.
How does gear ratio affect torque?
Torque is multiplied by the gear ratio. Output torque = Input torque × Gear ratio. For a ratio of 4:1 and input torque of 10 N·m, output torque is 40 N·m.

Tips & Common Mistakes

Tips

  • Ensure the driving and driven gear teeth counts are accurate; miscounting leads to incorrect ratios.
  • Use consistent units: input speed in rpm and torque in N·m for correct output calculations.
  • Remember that a gear ratio greater than 1 reduces speed and increases torque, while a ratio less than 1 increases speed and reduces torque.
  • Consider gear efficiency (typically 95-98%) for real-world applications, as friction losses reduce output torque.

Common Mistakes to Avoid

  • Reversing the order of teeth counts: the gear ratio is driven/driving, not driving/driven.
  • Forgetting to convert units if input speed is in rad/s or torque in lb-ft; this calculator expects rpm and N·m.
  • Assuming output speed and torque are independent; they are inversely related through the gear ratio.

Last updated: August 13, 2026