Vehicle Speed Calculator
Calculate your vehicle’s speed based on transmission gear ratios, tire size, and engine RPM
How Vehicle Speed Calculation Works
The formula to calculate vehicle speed is:
Where 336 is a constant factor that converts units appropriately.
Vehicle Speed
Frequently Asked Questions
Our calculator provides highly accurate results when correct inputs are provided. The calculation is based on standard mechanical formulas used in automotive engineering. However, real-world factors like tire wear, transmission efficiency, and road conditions may cause slight variations.
The gear ratio refers to the ratio in your transmission for a specific gear (e.g., 3rd gear ratio). The final drive ratio (also called axle ratio) is the ratio in your differential that reduces the rotational speed before it reaches the wheels. Both are multiplied together in speed calculations.
You can calculate tire diameter using the tire size code on the sidewall. For example, a tire marked “P265/70R17” would have a diameter calculated as: (265 × 0.70 × 2 ÷ 25.4) + 17 = approximately 31.6 inches. Alternatively, measure from the ground to the center of the wheel and double it.
Several factors can cause discrepancies: tire wear reduces diameter, transmission slip, torque converter efficiency, wheel spin, and even tire pressure. Speedometers themselves can be inaccurate by up to 5%. Always consider this calculation as a theoretical maximum under ideal conditions.
