Convert Tire Size
Convert tire size measurements between different units quickly and accurately
Tire Size Conversion Calculator
Popular Tire Size Conversions
Quickly convert between the most commonly used tire size units.
Understanding Tire Size Standards
Tire size conversions are essential for automotive maintenance, upgrades, and international vehicle standards. Different regions and manufacturers use various sizing systems (metric, imperial, flotation), and understanding these conversions is crucial for safe and optimal vehicle performance.
Common Tire Size Systems
Metric Sizing
- Width (mm) / Aspect Ratio (%) R Rim Diameter (in)
- Example: 225/60R16 = 225mm width, 60% aspect, 16in rim
Imperial & Flotation Sizing
- Overall Diameter (in) × Section Width (in) R Rim Diameter (in)
- Example: 31x10.50R15 = 31in diameter, 10.5in width, 15in rim
Common Applications
| Field | Tire Types | Typical Uses |
|---|---|---|
| Passenger Cars | Metric, Imperial | Standard road tires, all-season |
| Trucks/SUVs | Flotation, Metric | Off-road, all-terrain, mud-terrain |
| Motorsport | Metric, Custom | Racing slicks, performance tires |
| Motorcycles | Metric, Inch | Street, touring, off-road |
Conversion Tips
- 1 inch = 25.4 millimeters for diameter/width conversions
- Overall diameter = (Sidewall Height × 2) + Rim Diameter
- Sidewall Height = Section Width × (Aspect Ratio / 100)
- Always keep overall diameter within ±3% of original for speedometer accuracy
Tire Size Conversions
| Conversion | Formula | Quick Answer |
|---|---|---|
| mm to inches (width/diameter) | 1 mm = 0.0393701 in | Multiply mm by 0.0393701 |
| inches to mm (width/diameter) | 1 in = 25.4 mm | Multiply inches by 25.4 |
| Sidewall Height | Width × (Aspect Ratio / 100) | Multiply width by aspect ratio % |
| Overall Diameter | (Sidewall Height × 2) + Rim Diameter | Double sidewall height, add rim diameter |
| Circumference | Diameter × π | Multiply diameter by 3.1416 |
| Revolutions per mile | 63360 / Circumference (in) | Divide 63,360 by circumference in inches |
| Revolutions per km | 1000000 / Circumference (mm) | Divide 1,000,000 by circumference in mm |
| Flotation to Metric | (Overall Diameter × 25.4) / (1 + (Aspect Ratio / 100)) | Use for off-road tire conversions |
| Metric to Flotation | (Overall Diameter / 25.4) × (1 + (Aspect Ratio / 100)) | Use for off-road tire conversions |
Our tire size conversion tool provides accurate conversions between all major tire sizing systems, making it easy to upgrade, replace, or compare tires for any vehicle. Always consult manufacturer recommendations for safety and performance.
Tire Size Questions
Everything you need to know about tire size conversions
What do the numbers in tire sizes mean?
In metric sizing (e.g., 225/60R16), 225 is the width in millimeters, 60 is the aspect ratio (sidewall height as % of width), R means radial construction, and 16 is the rim diameter in inches. In flotation sizing (e.g., 31x10.50R15), 31 is overall diameter in inches, 10.50 is width in inches, and 15 is rim diameter.
Can I change my tire size safely?
You can change tire sizes, but the overall diameter should stay within ±3% of the original to maintain speedometer accuracy and avoid clearance issues. Wider tires may improve handling but can affect fuel economy. Always consult a tire professional for major size changes.
What's the difference between aspect ratio and sidewall height?
Aspect ratio is the percentage relationship between sidewall height and tire width. For example, in a 225/60 tire, the sidewall height is 60% of 225mm = 135mm. Lower aspect ratios (like 40) give shorter sidewalls and sportier handling, while higher ratios (like 70) provide more comfort.
How do I calculate my tire's overall diameter?
For metric tires: Overall diameter = (2 × sidewall height) + rim diameter. Sidewall height = tire width × (aspect ratio / 100). For example, 225/60R16: sidewall = 225 × 0.60 = 135mm, overall diameter = (2 × 135mm) + 406mm (16in) = 676mm or 26.6 inches.
Why is tire circumference important?
Tire circumference determines how far your vehicle travels with each wheel rotation, affecting speedometer readings, odometer accuracy, and gear ratios. If you change to a significantly different circumference, your speedometer will read incorrectly, and it may affect vehicle performance.
What are 'plus sizing' options in tires?
Plus sizing means using larger rims with lower-profile tires to maintain the same overall diameter. Plus 1 increases rim size by 1 inch and decreases sidewall height. This typically improves handling and appearance but may reduce ride comfort and increase road noise.
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