RPM to Speed Gear Ratio Calculator
Vehicle speed from engine RPM, gear ratio and tire size.
Enter your values
Enter the engine rpm in rpm.
Enter the transmission gear ratio you are working with.
Enter the final drive ratio you are working with.
Enter the tire diameter in in.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Vehicle speed
- 64.6 mph
- Wheel RPM
- 804.3
- Tire circumference
- 84.8 in
- Combined ratio
- 3.73
Quick answer
Vehicle speed is derived from engine RPM divided by the combined gear ratio, then converted using tire circumference.
speed (mph) = (RPM x tire diameter x pi x 60) / (gear ratio x final drive x 63360)
At a glance
| What it does | Vehicle speed from engine RPM, gear ratio and tire size. |
|---|---|
| Category | Automotive |
| Inputs needed | Engine RPM, Transmission gear ratio, Final drive ratio, Tire diameter |
| Main output | Vehicle speed |
| Formula | speed (mph) = (RPM x tire diameter x pi x 60) / (gear ratio x final drive x 63360) |
| Cost | Free — no sign-up, no download |
How to use the RPM to Speed Gear Ratio Calculator
- 1Enter engine RPM, the current gear ratio and final drive (axle) ratio.
- 2Enter the tire's overall diameter.
- 3The result converts engine speed into road speed using tire circumference.
Inputs explained
- Engine RPM(rpm)
- Enter the engine rpm in rpm.
- Transmission gear ratio
- Enter the transmission gear ratio you are working with.
- Final drive ratio
- Enter the final drive ratio you are working with.
- Tire diameter(in)
- Enter the tire diameter in in.
Worked example
Using the values the calculator loads with:
Inputs
- Engine RPM3000 rpm
- Transmission gear ratio1.0
- Final drive ratio3.73
- Tire diameter27 in
Results
- Vehicle speed64.6 mph
- Wheel RPM804.3
- Tire circumference84.8 in
- Combined ratio3.73
Frequently asked questions
Where do I find gear ratios?
Check your vehicle's service manual or a drivetrain specification sheet for each gear and the final drive ratio.
Why does tire size matter here?
A larger tire covers more ground per wheel revolution, increasing road speed for the same RPM.
What do I need to enter into the RPM to Speed Gear Ratio Calculator?
Just 4 values: engine rpm, transmission gear ratio, final drive ratio, tire diameter. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the RPM to Speed Gear Ratio Calculator work out the answer?
Vehicle speed is derived from engine RPM divided by the combined gear ratio, then converted using tire circumference. It applies the formula speed (mph) = (RPM x tire diameter x pi x 60) / (gear ratio x final drive x 63360) and shows the working so you can check each step by hand.
Is the RPM to Speed Gear Ratio Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.