Gear Ratio Calculator
Calculate gear ratios.
Input
Result
What is a Gear Ratio Calculator?
The Gear Ratio Calculator helps you calculate gear ratios between two gears for mechanical and automotive applications. Just enter your numbers and the tool does the rest — no manual math, no guesswork.
How to calculate Gear Ratio manually (the formula)
The specific formula depends on what you are calculating. The calculator applies the correct equation automatically, but understanding the formula helps you verify the results and adapt them to your own needs.
Example calculation
Enter your values into the calculator and it will produce an instant result. For a step-by-step walkthrough, try different inputs and observe how each one affects the outcome.
Common mistakes
- Reversing driver and driven — Always divide driven teeth by driver teeth, not the other way around.
- Ignoring multiple gear stages — For a gear train, multiply the ratios of each stage to get the total reduction.
- Confusing gear ratio with diameter ratio — For most calculations, tooth count matters more than physical diameter.
Frequently asked questions
What is gear ratio?
Gear ratio is the ratio of the number of teeth on two meshing gears. A 40-tooth gear driving a 10-tooth gear has a 4:1 ratio.
How do I calculate gear ratio?
Divide the number of teeth on the driven gear by the number of teeth on the driving gear. Ratio = Driven ÷ Driver.
What is the difference between gear ratio and final drive ratio?
Gear ratio is for one gear pair. Final drive ratio includes the differential and all gear reductions in the drivetrain.
How does gear ratio affect speed and torque?
A higher ratio (e.g., 4:1) increases torque but reduces speed. A lower ratio (e.g., 2:1) increases speed but reduces torque.
What does a higher gear ratio mean?
Higher gear ratio means the engine turns more times per wheel rotation. Better acceleration, lower top speed.
How do I calculate RPM from gear ratio?
Output RPM = Input RPM ÷ Gear Ratio. If the engine is at 3000 RPM with a 3:1 ratio, the wheel spins at 1000 RPM.