Engine RPM to Vehicle Speed: Sizing Tires & Gear Ratios

To determine how fast a vehicle travels at a specific engine RPM, you must calculate how many times the tires rotate based on the transmission ratio, final drive ratio, and tire diameter.

The Speed Formula

Vehicle speed in miles per hour (mph) is calculated using this formula:

$$\text{Speed (mph)} = \frac{\text{RPM} \times \text{Tire Diameter (inches)}}{\text{Gear Ratio} \times \text{Final Drive} \times 336}$$

For example, an engine spinning at 3,000 RPM with a 1.00 gear ratio, 3.73 final drive, and 26-inch tires is traveling at approximately 62 mph ((3000 \times 26 \div (1.00 \times 3.73 \times 336) = 62.2\)).

Simulate your vehicle's speed at different RPMs using our interactive automotive gear ratio calculator. For gearbox comparisons, read our guide on close-ratio vs. wide-ratio transmissions.