How it works
Calculate exact tire dimensions from standard sidewall codes.
Input query strings and outputs
Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.
Input query strings
3-
?width=Width (mm)Number · Optional · Default: 225
-
?ratio=Aspect RatioNumber · Optional · Default: 45
-
?diameter=Diameter (in)Number · Optional · Default: 17
Outputs
1-
resultResultText · Primary output
result contains the calculator’s complete rendered result area, including its visible result cards, tables, charts, and messages.
Calculate the actual height, width, and circumference of a vehicle’s tire
Description
The Tire Size Calculator is a technical tool for car owners, mechanics, and off-road enthusiasts. Tires are labeled with a cryptic code (like 225/45 R17) that mixes metric millimeters, percentages, and imperial inches. This tool decodes these numbers into usable measurements: the actual Height (diameter), the Width (section width), and the Circumference (the distance covered in one full rotation).
Inputs
- Width (mm): The first number in the code (e.g.,
225). - Aspect Ratio: The second number, representing sidewall height as a % of width (e.g.,
45). - Diameter (in): The final number, representing the wheel/rim size (e.g.,
17).
Outputs
- Total Diameter (Height): The total vertical size of the tire in inches.
- Width: The actual width of the tire tread in inches.
- Circumference: The rolling distance in inches.
Chart
- N/A: This tool provides precision numeric automotive results.
“Good to Know”
- Sidewall Height: Calculated as: $Width \times (Aspect Ratio / 100)$. One tire has two sidewalls (top and bottom), which are added to the rim size.
- Speedometer Accuracy: If you change to a tire with a different diameter, your speedometer will be incorrect because your car thinks a rotation covers a different distance than it actually does.
- Visual Check: A “low profile” tire (small aspect ratio) has a shorter sidewall, which often looks better but providing a firmer (and sometimes rougher) ride.
Examples
Example 1: Standard Sedan
- Input: 225 / 45 R17
- Output: Height: 24.97”, Width: 8.86”, Circumference: 78.45”
Example 2: Large SUV/Truck
- Input: 265 / 70 R18
- Output: Height: 32.61”, Width: 10.43”, Circumference: 102.44”
Example 3: Performance Sports Car
- Input: 305 / 30 R20
- Output: Height: 27.20”, Width: 12.01”, Circumference: 85.46”