Tire Size Calculator

In the automotive world, selecting the right tire size for your vehicle is crucial for ensuring safety, optimal performance, and an enjoyable driving experience. This is where the utility of a tire size calculator tool becomes indispensable, particularly if you are contemplating a change in tire size for aesthetic enhancements, performance improvements, or simply as a replacement.

Our user-friendly tire size calculator assists you in determining the diameter, width, sidewall height, and circumference of any tire, offering results in both metric and imperial units. Simply choose your tire size type, input the specs, and hit calculate. Not sure what your tire size means? Follow our quick guide on how to read tire size. Additionally, a comprehensive tire size chart is also available for reference.

It's important to note that the calculations provided by our tool are based on the tire size entered and may not reflect the exact specifications of all tire models. Since tire dimensions can vary slightly between manufacturers, we recommend consulting the manufacturer's guidelines for precise tire specifications.

Are you thinking about replacing or upgrading your tires and need to understand how different sizes will impact your vehicle? Our tire size comparison tool is designed for this purpose. It helps you grasp the effects of varying tire sizes, ensuring that your choice maintains safety, compatibility with your vehicle, and delivers the best possible performance.

How to calculate tire width

The width of a tire is the distance across the broadest part of the tire's tread, indicating the contact patch area - the part of the tire that actually touches the road. It is a critical parameter in vehicle dynamics, influencing aspects such as traction, handling, fuel efficiency, and ride comfort.

Wider tires generally provide better traction and handling due to a larger contact area with the road surface, which can improve vehicle stability, especially during cornering, acceleration, and braking. However, this comes at the expense of increased air resistance and potentially lower fuel efficiency, as wider tires can create more rolling resistance. The choice of tire width also affects ride comfort; wider tires can offer a smoother ride by better absorbing road imperfections, though this can vary based on tire construction and the vehicle's suspension system. It's important to choose a tire width appropriate for the vehicle and its intended use, as overly wide tires can cause problems with fitment, potentially rubbing against the vehicle's body or suspension components, while too narrow tires might not support the vehicle's weight or performance characteristics adequately.

To calculate the width of a tire, you typically do not need to do any complex calculations, as the width is usually directly provided as part of the tire size code. Here is how to read and understand it:

• In a metric tire size, tire width is the first number in the size marking and is measured in millimeters. For example, in a tire size code P215/60R16, the width of the tire is 215 millimeters.
• In a flotation tire size, tire width is also provided in the size marking, but it is usually in inches. For example, in 35x12.50R17, the width of the tire is 12.5 inches.
• To convert tire dimensions from millimeters to inches and vice versa, you can use the conversion factor: 1 inch is approximately 25.4 millimeters. So, to convert millimeters to inches, divide the number by 25.4. To convert inches to millimeters, multiply the number by 25.4. For example, a tire width of 215 millimeters is approximately 8.5 inches (215 / 25.4 = 8.5). And a tire width of 12.5 inches is approximately 318 millimeters (12.5 x 25.4 = 318). For more information, check out the tire size converter.

How to calculate tire sidewall height

The sidewall height of a tire refers to the vertical distance from the edge of the wheel rim to the outer tread of the tire. The sidewall height is indirectly indicated in a tire's size designation through the aspect ratio. It is a key component in determining the overall size, comfort, and performance characteristics of the tire.

The sidewall height affects the tire's performance and the vehicle's handling. A lower aspect ratio (shorter sidewall) usually means better handling and cornering but a firmer ride, while a higher aspect ratio (taller sidewall) typically provides a softer, more comfortable ride but with less precise handling.

Here is how the sidewall height of a tire is calculated:

• For a metric tire size such as P215/60R16, identify the aspect ratio of a tire. The aspect ratio is the number after the slash, which in our example is 60. The aspect ratio is a percentage that represents the height of the tire's sidewall relative to the tire's width. To calculate the sidewall height, you take the aspect ratio and apply it to the width of the tire. For example, in P215/60R16, the sidewall height can be calculated as 60% of 215 mm (the width of the tire), which is 129 millimeters.
• Calculating the sidewall height for a flotation tire size involves a slightly different approach compared to standard metric tire sizes. The sidewall height for a flotation tire is half the difference between the overall diameter and the rim diameter. Since these are already in inches, the calculation is straightforward. For example, with a tire size of 35x12.50R17, the overall diameter is 35 inches, and rim diameter is 17 inches. To find the sidewall height, you need to subtract the wheel diameter from the overall tire diameter and then divide in half ((35 - 17) / 2), giving us 9 inches.

How to calculate tire diameter

Tire diameter, also known as tire height, is the total height of the tire from the ground to the top of the tire when it's mounted on a wheel and inflated. This measurement is crucial as it affects various aspects of a vehicle's performance, including speedometer accuracy, gearing, and ground clearance.

The overall diameter of a tire affects how the vehicle rides and handles. A larger diameter tire will generally have a longer contact patch with the road, potentially improving grip and stability, but can also affect the speedometer reading and the vehicle's effective gearing. When replacing tires, it is recommended to stick close to the original tire diameter specified by the vehicle manufacturer to maintain the intended performance and safety characteristics of the vehicle.

Calculating the tire diameter for both metric and flotation tire sizes involves different methods due to the way these sizes are expressed. Here's how you can calculate the diameter for each:

• For a metric tire size like P215/60R16, the tire diameter can be calculated using the width, aspect ratio, and wheel diameter. The tire diameter is the sum of twice the sidewall height plus the diameter of the wheel. Since wheel diameter is most likely in inches, multiply it by 25.4 to get equivalent value in millimeters. Formula is as follows: Tire Diameter = 2 x (Tire Width x (Aspect Ratio / 100)) + (Wheel Diameter x 25.4). So, for P215/60R16 tire size, the overall diameter would be calculated as 2 x (215 x (60 / 100)) + (16 x 25.4) = 664 millimeters or 26.2 inches.
• In a flotation tire size like 35x12.50R17, the first number is the overall diameter of the tire in inches. In our example, the tire diameter is 35 inches. To convert that number to millimeters, multiply it by 25.4 (35 x 25.4 = 889 mm).

How to calculate rim diameter

Rim diameter refers to the diameter of the wheel on which the tire is mounted. It is an essential measurement in the tire size designation and plays a crucial role in determining which tires will fit a particular vehicle. Rim diameter is measured from one edge of the wheel's seating surface (where the tire bead sits) to the opposite edge, crossing through the center of the wheel. This measurement is typically provided in inches.

For both metric and flotation tire sizes, the rim diameter is indicated by the last number in the tire code. For example, P215/60R16 has a rim diameter of 16 inches, and 35x12.50R17 has a wheel diameter of 17 inches.

How to calculate tire circumference

Tire circumference indicates the total distance around the outer tread of the tire - essentially, the distance a tire covers in one full revolution. This measurement is crucial for the accurate functioning of the vehicle's speedometer and odometer. If the tire circumference changes significantly (due to changing tire sizes), it can lead to incorrect speedometer and odometer readings.

To calculate the tire circumference, you need to know the tire's diameter. Once the diameter is determined, you can use the formula for the circumference of a circle: Circumference = π x Diameter, where π (pi) is approximately 3.1416.

How to calculate tire revolutions

Tire revolutions is a key metric that indicates how many times a tire will rotate over the course of traveling a specific distance, directly impacting vehicle dynamics such as speedometer accuracy, fuel efficiency, and overall vehicle performance. This value is inherently tied to the tire's size, specifically its circumference, as a tire with a larger overall diameter will cover more ground per revolution than a smaller one.

Tire revolutions are crucial in calculating speedometer and odometer readings, and understanding vehicle dynamics. Vehicle's speedometer is calibrated based on the standard size of tires for that vehicle. It calculates speed by counting the number of tire revolutions per minute and then uses the tire circumference to convert this into a travel speed. Changing tire sizes can alter the number of revolutions a tire makes, impacting the accuracy of your vehicle's speedometer and odometer. Using our speedometer calibration tool will give you a rough idea of how much your speedometer is off due to a tire size change.

To calculate the number of tire revolutions per mile or kilometer, you need to know the tire's circumference. Once you have the circumference (either by calculation or from manufacturer specifications), divide the distance (one mile or one kilometer) by the tire's circumference.

Revolutions per Mile = Number of Inches in a Mile / Tire Circumference in Inches.

Revolutions per Kilometer = Number of Millimeters in a Kilometer / Tire Circumference in Millimeters.

All listed guides, data and/or calculations are for informational purposes only. TireSizes.com does not warrant or make any representations regarding the accuracy of or the results of the use of this information.