How to Measure the Outside Diameter of Tires


When replacing your tires, it is necessary to know their outside diameter, or the distance across the widest part of the tire. If you want to accessorize your tires with rims or other adornments, you will also need to know the tire’s measurement. The diameter of the tires that comes standard on a vehicle is always listed in the operating manual, but if you do not have the vehicle’s manual, you will need to measure the outside diameter of the tire yourself.

Things You'll Need

  • Tape measure or long ruler
  • Place the starting point of the tape measure or long ruler on the ground where the tire sits. If you are using a tape measure, there will be a small tab that sticks out or can be folded over so you can hold the tape measure in place. If you are using a ruler, simply put the end of the ruler directly on the ground in front of the tire.

  • Make sure the tape measure or ruler is lined up with the center of the tire as closely as possible. Use the center circle on the hubcap or the center hole in the tire mount to help find the tire’s center. You will need to measure near the center of the tire to get an accurate measurement.

  • Hold the tape measure or ruler vertically. Take the measurement from the bottom of the tire to the outside edge of the top of the tire.

  • Round the measurement up to the nearest whole inch, even if the measurement is closer to the next inch below. For instance, if the tire measures 14.2 inches, round it up to a 15-inch diameter, even though the actual measurement is closer to 14 inches. Most tire measurements are done in whole inches and the weight of the vehicle can press the tire down slightly.

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