Transmission Calculator
Table of contents
What are transmission gear ratio and differential gear ratio?How do I calculate transmission gear ratiosHow to use transmission gear ratio calculatorFAQsOur transmission calculator is designed to help you answer key questions like, "How do I calculate transmission gear ratios?" and "How do I find the right transmission ratio?" Whether you're looking to calculate RPM or determine the ideal gear ratios for your vehicle, our tool has the answers! Input your values, and let the calculator do the math for you.
What are transmission gear ratio and differential gear ratio?
Ever wondered how your car moves? Well, it's powered by its engine, but how does the engine make the wheels turn? This is where transmission and differential gear ratios come into play. Our calculator can help you figure out these concepts, especially if you're interested in the mechanics behind them.
So, what do these terms even mean?

The transmission gear ratio is basically how your car decides the speed at which the wheels turn based on how fast the engine is spinning.

The differential gear ratio (aka ring and pinion ratio) controls how the engine’s power is distributed to the wheels, which is important for your car’s acceleration. These ratios are all about balancing power and speed to ensure your car runs smoothly.
If you’re just getting started with understanding gears, maybe start with something simpler like our bike gear calculator. And if you feel like this calculator is perfect for you, continue reading this article to learn everything about this topic!
How do I calculate transmission gear ratios
Alright, so how do I calculate transmission gear ratios? How do I find the right transmission ratio, and how do I calculate RPM? It’s not as hard as it may seem.
For example, to calculate the transmission gear ratio, you take the number of teeth on the driven gear and divide it by the number of teeth on the driving gear. That's the basic idea.
When using our transmission calculator, you’ll have to input various values such as engine RPM, transmission gear ratio, differential gear ratio, and tire diameter. Then, boom, you'll get the speed.
Our transmission gear ratio calculator uses just this one formula to calculate your output:
Speed (km/h) = Engine RPM × Tire Diameter (mm) × π × 60 × Transmission Gear Ratio × Differential Gear Ratio × 1000000
This might look complicated, but it’s really just turning engine power into how fast your car goes, considering all the gears. Simple, right?
If we've sparked your curiosity about gears and how they work, feel free to check out our gear ratio calculator to learn more about this topic!
How to use transmission gear ratio calculator
The transmission gear ratio calculator is easy to use, and it works like this:

Differential gear ratio — First, input the ratio of your differential gears. This value determines how the engine's power gets to the wheels. The right ratio makes a big difference in your car’s performance.

Tire diameter — Next, enter the diameter of your tires in inches or any other chosen unit. The tire size determines how far your vehicle travels with each wheel rotation.

Engine RPM — Then, you need to enter the engine’s RPM. This is simply how fast your engine is turning at any given moment. A higher RPM generally means more speed. You can experiment with this value to see your vehicle's speed at different revs.

Transmission gear ratio — Finally, input the transmission gear ratio for the gear you’re using. This ratio converts the engine RPM into wheel RPM, and that’s what drives the car forward.
Once you’ve entered all these values, the calculator will give you the vehicle speed in kilometers per hour. Just plug in the numbers, and the result is there. Have fun with your calculations!
💡 Enjoyed using our calculator? If so, be sure to check out our other tools for speed enthusiasts, like our race predictor or turbo size calculator!
How do I calculate RPM?
To calculate RPM (revolutions per minute), you'll need to measure the frequency of rotations per minute like this:
 Count the number of rotations in a given amount of time.
 Divide that number by the time in minutes.
 You'll then have calculated the RPM.
What's the tire diameter for standard passenger car?
The tire diameter for a standard passenger car typically ranges from 24 to 28 inches. This size varies based on the car model and type of tires used.
What tire diameter to achieve a speed of 120 km/h at 5000 RPM?
To achieve a speed of 120 km/h at 5000 RPM, with a transmission gear ratio of 1 and a differential gear ratio of 3, you would need approximately a 15inch tire. However, this depends on many factors, such as vehicle type, load, and tire design.
What is the vehicle speed with 6000 RPM and 1.5 transmission ratio?
With a tire diameter of 26 inches, a differential gear ratio of 3, and an engine RPM of 6000 with a transmission ratio of 1.5, the vehicle speed would be approximately 103 mph.