Calculated tire dimensions
Use the comparison calculator to check diameter, width, ride-height and speedometer differences.
How the Tire Size Calculator Works
Enter a metric tire size such as 285/70R17 or a flotation size such as 35x12.5R20. The calculator converts the size notation into useful tire dimensions, including overall diameter, section width, sidewall height, circumference and approximate revolutions per mile.
Metric Tire Size Example: 285/70R17
| Part | Meaning |
|---|---|
| 285 | Nominal section width in millimeters |
| 70 | Sidewall height as a percentage of tire width |
| R | Radial tire construction |
| 17 | Wheel diameter in inches |
Flotation Tire Size Example: 35x12.5R20
| Part | Meaning |
|---|---|
| 35 | Nominal overall tire diameter in inches |
| 12.5 | Nominal section width in inches |
| R | Radial tire construction |
| 20 | Wheel diameter in inches |
Tire Size Calculator FAQ
How is overall tire diameter calculated?
For a metric size, sidewall height is width multiplied by the aspect ratio. Two sidewalls are added to the wheel diameter. For flotation sizes, the stated nominal overall diameter is used directly.
Why can a real tire measure differently from the calculator?
Tire-size notation describes nominal dimensions. Actual mounted size can vary by manufacturer, tread design, approved wheel width, inflation pressure and load.
What does revolutions per mile mean?
Revolutions per mile estimates how many complete tire rotations occur over one mile based on calculated circumference. Manufacturer-published revs per mile can differ from pure geometric calculations.
Can I use these calculations to confirm vehicle fitment?
No. Tire dimensions are only part of fitment. You must also verify the exact vehicle, wheel dimensions, load requirements, clearances and manufacturer recommendations.