Figure out the speed, RPM, and overall gear ratio for every gear in your transmission. Enter your gear ratios, final drive, tire diameter, and engine RPM, get a complete breakdown in seconds.
| Gear | Transmission Ratio | Overall Ratio | RPM (at speed) | Speed (mph) |
|---|
Enter details and calculate to see gear ratio table.
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Whether you’re building a custom transmission, swapping gears, or simply trying to understand how your vehicle’s drivetrain works, knowing the relationship between transmission gear ratios, final drive, tire size, and engine RPM is essential. The gear ratios determine how engine power is delivered to the wheels, affecting acceleration, top speed, and highway cruising RPM. Getting the numbers right helps you choose the right transmission for your application, whether it’s a drag car, a street machine, or a daily driver.
This transmission gear ratio calculator gives you a complete view of your drivetrain. Enter up to six transmission gear ratios, the final drive ratio, tire diameter, and engine RPM. The tool computes the overall ratio for each gear, the speed at your specified RPM, and displays everything in a clear summary and a detailed gear ratio table. Whether you’re a mechanic setting up a new transmission, a builder planning a drivetrain, or an enthusiast analyzing your vehicle’s performance, this calculator delivers the answers you need. All calculations run locally in your browser, keeping your data private.
Select your unit system: Imperial (mph, in) or Metric (km/h, mm) from the dropdown at the top.
Enter the gear ratio for each transmission gear from 1st through 6th leave any unused gears at zero.
Enter the final drive ratio (rear axle ratio), for example, 3.42:1 for many trucks and performance cars.
Enter the tire diameter, the overall diameter of your tire (including the sidewall).
Enter the engine RPM at which you want to calculate speed typically the peak horsepower RPM or redline.
Review the summary results and the detailed gear ratio table showing every gear’s ratio, overall ratio, RPM, and speed.
The calculator applies the standard formula for the relationship between engine RPM, vehicle speed, gear ratio, and tire diameter. This formula is used by automotive engineers and mechanics to understand drivetrain dynamics.
Formula: Overall Ratio = Transmission Gear Ratio × Final Drive Ratio
Formula: Speed = (RPM × Tire Diameter) / (Overall Ratio × 336)
Formula: RPM = (Speed × Overall Ratio × 336) / Tire Diameter
The constant 336 comes from the conversion between miles per hour, inches, and minutes. It’s derived from: (63,360 inches per mile ÷ 60 minutes per hour) ÷ π ≈ 336. Tire diameter must be in inches, speed in miles per hour, and RPM is revolutions per minute.
For metric units, speed is converted to mph and tire diameter to inches before calculation, with results displayed in your selected unit system.
Consider a 6-speed transmission with the following gear ratios: 1st 3.50:1, 2nd 2.20:1, 3rd 1.50:1, 4th 1.10:1, 5th 0.80:1, 6th 0.65:1. The final drive is 3.42:1, tire diameter is 28 inches, and engine RPM is 6,000. Let’s analyze the performance.
Step 1: Calculate overall ratio for each gear
1st: 3.50 × 3.42 = 11.97:1
2nd: 2.20 × 3.42 = 7.52:1
3rd: 1.50 × 3.42 = 5.13:1
4th: 1.10 × 3.42 = 3.76:1
5th: 0.80 × 3.42 = 2.74:1
6th: 0.65 × 3.42 = 2.22:1
Step 2: Calculate speed at 6,000 RPM
1st: (6000 × 28) / (11.97 × 336) = 168,000 / 4,022 = 41.8 mph
6th: (6000 × 28) / (2.22 × 336) = 168,000 / 746 = 225.2 mph
Interpretation: At 6,000 RPM, this vehicle would reach about 42 mph in 1st gear and about 225 mph in 6th gear (theoretically). The overall ratio of 11.97:1 in 1st gear provides massive torque multiplication for strong acceleration, while the 2.22:1 ratio in 6th gear provides low RPM cruising at highway speeds.
Transmission gear ratio is the relationship between the input shaft and output shaft in a specific gear. It’s the number of times the input shaft turns for each revolution of the output shaft.
Overall gear ratio is the transmission gear ratio multiplied by the final drive ratio. For example, a 3.50:1 1st gear and a 3.42:1 final drive gives an overall ratio of 11.97:1.
Transmission gear ratio is the ratio inside the transmission for a specific gear. Final drive ratio is the ratio in the differential (rear axle). The overall ratio is the product of both.
Larger tires effectively lower the overall gear ratio because they cover more distance per revolution. This reduces engine RPM at a given speed and lowers torque at the wheels. To maintain performance with larger tires, a lower (numerically higher) final drive ratio is often needed.
A good 1st gear ratio depends on the vehicle’s weight and intended use. For a typical street car, 3.00–4.00:1 is common. For a drag car, 4.00–5.00:1 or higher is often used. The calculator helps you see the effect of different ratios.
A good top gear ratio depends on the vehicle’s use. For highway cruising, 0.60–0.80:1 provides low RPM at speed. For performance applications, 0.85–1.00:1 keeps the engine in the power band at higher speeds. The calculator helps you compare options.
Transmission gear ratios can be found in the vehicle’s owner’s manual, service manual, or by searching online for your transmission model. You can also calculate them by counting teeth on the gears or using a tachometer and speedometer.
The 336 constant comes from the conversion between miles per hour, inches, and minutes. It’s derived from: (63,360 inches per mile ÷ 60 minutes per hour) ÷ π ≈ 336. This constant is used when speed is in mph and tire diameter is in inches.
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