Tire Size Calculator
Calculate tire diameter, circumference, and sidewall height from the metric tire size designation.
This free online tire size calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.
Section width in mm (first number, e.g. 225 in 225/45R17).
Sidewall height as percentage of width (e.g. 45 in 225/45R17).
Wheel diameter in inches (e.g. 17 in 225/45R17).
Results
Overall Diameter
25 in
Overall Diameter
634 mm
Sidewall Height
101.3 mm
Circumference
1993 mm
How to Use This Calculator
Enter your input values
Fill in all required input fields for the Tire Size Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.
Review your inputs
Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.
Read the results
The Tire Size Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.
Explore parameter sensitivity
Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.
Formula Reference
Tire Size Calculator Formula
See calculator inputs for the governing equation
Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.
When to Use This Calculator
- •Use the Tire Size Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
- •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
- •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
- •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.
About This Calculator
The Tire Size Calculator is a free, browser-based calculation tool for engineers, students, and technical professionals. Calculate tire diameter, circumference, and sidewall height from the metric tire size designation. It implements standard formulas and supports both metric (SI) and imperial unit systems with automatic unit conversion. All calculations are performed instantly in your browser with no data sent to a server. Use this calculator as a quick reference and sanity-check tool during design, analysis, and learning. Always verify results against primary engineering references and applicable standards for any safety-critical application.
About Tire Size Calculator
Tire sizes are expressed in a cryptic-looking designation like 225/45R17, but once decoded, these numbers tell you everything about the tire's dimensions. The Tire Size Calculator converts the metric tire size into practical measurements: overall diameter, sidewall height, and circumference. These dimensions matter when upgrading wheels, ensuring proper speedometer calibration, and checking that replacement tires fit your vehicle without rubbing on fenders or suspension components. The first number (225) is the section width in millimeters, the second (45) is the aspect ratio (sidewall height as a percentage of width), and the last (17) is the rim diameter in inches.
The Math Behind It
Formula Reference
Tire Diameter
Diameter = Rim(in) x 25.4 + 2 x Width(mm) x AspectRatio/100
Variables: Width in mm; AspectRatio as percentage; Rim in inches; result in mm
Worked Examples
Example 1: Decode a 225/45R17 tire
Find the dimensions of a 225/45R17 tire.
The tire is about 25.0 inches in diameter with a 1993 mm circumference.
Common Mistakes & Tips
- !Forgetting to multiply sidewall height by 2 (there is a sidewall on both the top and bottom of the tire).
- !Confusing the aspect ratio with the sidewall height in mm.
- !Not checking for fender clearance when upsizing tires.
Related Concepts
Frequently Asked Questions
What does the R in tire size mean?
R stands for Radial construction, which is the standard tire construction method used in virtually all modern passenger vehicles. The cords in the tire body run radially from bead to bead.