Tire Size Conversion - Convert Metric, Imperial, and Flotation Tire Sizes
Tire Size Converter
Convert tire size measurements between different units quickly and accurately
Convert Tire Size
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
How do I read tire size markings like 225/60R16?
This format shows: 225 = tire width in millimeters, 60 = aspect ratio (sidewall height as percentage of width), R = radial construction, 16 = rim diameter in inches. So this tire is 225mm wide, sidewall height is 60% of 225mm (135mm), and fits a 16-inch rim.
What is tire aspect ratio and how does it affect performance?
Aspect ratio is the sidewall height as a percentage of tire width. Lower ratios (like 40) mean shorter sidewalls for better handling and responsiveness but harsher ride. Higher ratios (like 70) provide more comfortable ride but less precise handling. Common ratios: 40-50 for performance, 60-70 for comfort, 75+ for trucks.
Can I change tire sizes on my car?
You can change sizes within limits, but maintain the same overall diameter (±3%) to avoid speedometer error and clearance issues. You can typically go wider with lower aspect ratio, or narrower with higher aspect ratio. Always check load rating, speed rating, and vehicle clearances. Consult tire professionals for safety.
How do plus sizing and minus sizing work?
Plus sizing: larger rim diameter with lower profile tire (225/60R16 → 225/50R17). Minus sizing: smaller rim with higher profile tire. Both aim to maintain overall diameter. Plus sizing improves handling but reduces comfort and increases cost. Minus sizing does the opposite.
What's the difference between metric and imperial tire sizing?
Metric uses millimeters for width and percentage for aspect ratio (225/60R16). Imperial/flotation uses inches for all dimensions (31x10.50R15 = 31" diameter, 10.5" width, 15" rim). Some older systems use different formats. Metric is most common worldwide for passenger cars.
How does tire diameter affect my speedometer?
Speedometer accuracy depends on overall tire diameter. Larger diameter makes speedometer read slower than actual speed; smaller diameter makes it read faster. A 3% change in diameter equals 3% speedometer error. For example, if your speedometer reads 60 mph with 3% larger tires, you're actually going 61.8 mph.
What are run-flat tires and how do they affect sizing?
Run-flat tires have reinforced sidewalls that support the vehicle even when deflated. They're typically marked with 'RFT', 'ROF', or similar. Run-flats may have slightly different dimensions than standard tires of the same size marking due to construction differences. They often require specific wheels and can't always be replaced with standard tires.
How do I calculate tire circumference and revolutions per mile?
Circumference = π × diameter. For revolutions per mile: divide 5,280 feet (1 mile) by tire circumference in feet, or divide 63,360 inches by circumference in inches. This affects speedometer calibration and odometer accuracy. Tire manufacturers provide exact revolutions per mile data for precision applications.
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