Speedometer Gear Calculator

The “Speedometer Gear Calculator” is a handy tool designed to assist you in determining the appropriate gear teeth for your speedometer.

Speedometer Gear Calculator

Speedometer Gear Calculator Tool

How to Calculate Speedometer Gear Teeth

To calculate the speedometer gear teeth, you would typically need the following information:

  1. Tire Diameter: Measure the diameter of the tires on your vehicle in inches. This measurement represents the height of the tire from the ground to the top of the tire.
  2. Axle Ratio: The axle ratio refers to the number of revolutions the driveshaft makes compared to the axle or wheel revolutions. It is usually denoted as a ratio (e.g., 3.73:1).
  3. Desired Speedometer Accuracy: Determine the level of accuracy you want for your speedometer. This is typically expressed as a percentage. For example, if you want the speedometer to be accurate within 2%, the desired accuracy would be 2.

The formula to calculate the speedometer gear teeth is:

Speedometer Gear Teeth = (Drive Teeth * Axle Ratio * 63360) / (Tire Diameter * Desired Accuracy)


  • Drive Teeth: Number of teeth on the drive gear (typically located on the transmission output shaft or a sensor).
  • Axle Ratio: The ratio of the number of teeth on the ring gear to the pinion gear in the differential.
  • 63360: Conversion factor to convert inches to miles (12 inches in a foot, 5280 feet in a mile).
  • Tire Diameter: The measured diameter of the tire in inches.
  • Desired Accuracy: The desired accuracy of the speedometer reading as a percentage.

By plugging in the values for drive teeth, axle ratio, tire diameter, and desired accuracy into the formula, you can calculate the appropriate number of teeth for the speedometer gear.