Enter your engine RPM, transmission gear ratio, rear axle ratio, and tire height to find your vehicle's output speed in MPH. The Gear Ratio Speed Calculator also shows you the effective overall drive ratio and helps you understand how gear and tire changes affect your speed.
Vehicle Speed
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Overall Drive Ratio
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Transmission Output Shaft RPM
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Wheel (Axle) RPM
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A gear ratio describes how many times the input shaft (engine) rotates for every one rotation of the output shaft. A higher gear ratio (like 3.54:1) multiplies torque but reduces output speed, while a lower ratio (like 0.70:1 overdrive) allows higher output speeds for a given engine RPM.
Larger tires have a greater circumference, so each wheel revolution covers more ground. Running taller tires than your vehicle was geared for will make your speedometer read lower than your actual speed and effectively lower your overall drive ratio, reducing acceleration but improving highway cruising.
The rear axle ratio is the number of times the driveshaft rotates for every one rotation of the rear wheels. It is determined by the number of teeth on the ring gear divided by the number of teeth on the pinion gear. Common ratios range from 2.73:1 to 4.56:1.
The overall drive ratio is the transmission gear ratio multiplied by the rear axle ratio. For example, a 2.00 transmission ratio combined with a 3.73 axle ratio gives an overall ratio of 7.46:1, meaning the engine spins 7.46 times for every one revolution of the rear wheels.
Enter the engine RPM at the operating condition you want to evaluate. Common examples include highway cruising RPM (typically 1,800–2,500 RPM), peak power RPM, or maximum RPM (redline). This tells you the vehicle speed at that specific engine speed in the selected gear.
Tire height can be read from the tire sidewall markings or calculated using a tire height calculator. For a tire labeled 265/70R17, the formula is: (2 × (265 × 0.70 / 25.4)) + 17 ≈ 31.6 inches. You can also physically measure the overall diameter of a mounted, inflated tire.
A numerically higher axle ratio (e.g., switching from 3.08 to 4.10) improves low-speed acceleration and towing capability but increases engine RPM at highway speeds, reducing fuel economy. A numerically lower ratio (e.g., 2.73) lowers highway RPM and improves fuel economy but sacrifices off-the-line power.
Yes. Simply enter the gear ratio for whichever gear you want to evaluate — whether it's from a manual, automatic, or CVT transmission. Refer to your vehicle's transmission specification sheet or owner's manual to find the individual gear ratios for each gear.