This tire size calculator helps estimate important tire dimensions based on width, aspect ratio, and rim diameter. Use it either to calculate a single tire’s specifications or to compare two tire sizes and see the difference in diameter, circumference, and speedometer reading.
Tire Size Calculator
Select a mode below. A standard tire size uses three main numbers: width in millimeters, aspect ratio as a percentage of width, and rim diameter in inches. The calculator converts these into sidewall height, total diameter, circumference, and related tire measurements.
What is a Tire Size Calculator?
A tire size calculator converts tire dimensions into more useful measurements such as sidewall height, overall diameter, circumference, and revolutions per mile. It can also compare two different tire sizes to show how much they differ.
Main Formula
The basic process is:
Sidewall Height (in) = Sidewall Height (mm) ÷ 25.4
Overall Diameter = Rim Diameter + 2 × Sidewall Height (in)
Circumference
Once the overall diameter is known, the tire circumference is:
How to Use It
Use Tire Specs when you want to calculate dimensions for one tire size. Use Compare Tires when you want to see the diameter change, percentage difference, and speedometer impact between your current tire and a new tire size.
Example Tire Sizes
| Tire Size | Sidewall | Diameter | Circumference |
|---|---|---|---|
| 205/55R16 | 4.44 in | 24.88 in | 78.16 in |
| 225/45R17 | 3.99 in | 24.97 in | 78.45 in |
| 235/40R18 | 3.70 in | 25.40 in | 79.80 in |
| 245/75R16 | 7.23 in | 30.47 in | 95.73 in |
| 285/70R17 | 7.85 in | 32.70 in | 102.73 in |
Important Note
This calculator provides geometric estimates. Real-world mounted tire dimensions can vary by manufacturer, tread design, load, inflation pressure, and measuring standards. Always verify fitment, clearance, and load rating before changing tire sizes.