Tire Size Converter: Metric to Inches & Inch to Metric
Enter a metric tire size such as 265/70R17 to calculate its nominal diameter, width, and sidewall height in inches. You can also enter a flotation size such as 35×12.50R17LT to see its nominal dimensions and nearby calculated metric sizes.
Tire size converter
Convert between metric and flotation tire dimensions. Choose your conversion below.
Format: width / aspect ratio R wheel diameter. Example: 265/70R17
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Calculated nominal dimensions
Dimensions are calculated from the size designation. They are not measurements of a particular tire. Theoretical revolutions per mile may differ from published or measured rolling values.
A close dimensional match does not establish fitment. Check the vehicle placard or owner's manual, tire load and speed ratings, wheel compatibility, clearance, and manufacturer guidance.
Quick Answer: A tire size converter translates dimensions from a tire-size designation. A metric size gives section width in millimeters, aspect ratio, and wheel diameter. A flotation size gives nominal overall diameter and section width in inches, plus wheel diameter. A nearby calculated size is not an exact replacement or a fitment approval.
How to Convert a Metric Tire Size to Inches
Take 265/70R17 as an example. The 265 is nominal section width in millimeters; 70 is the aspect ratio, meaning the sidewall height is 70% of the width; and 17 is the nominal wheel diameter in inches. The R denotes radial construction.
| Calculation | Result |
|---|---|
| Section width: 265 ÷ 25.4 | 10.43 in |
| Sidewall height: 265 × 0.70 | 185.5 mm, or 7.30 in |
| Nominal diameter: 17 + (2 × 185.5 ÷ 25.4) | 31.61 in |
| Nominal circumference: unrounded diameter × π | 99.29 in |
Therefore, 265/70R17 calculates to approximately 31.61 inches tall and 10.43 inches wide. These are dimensions calculated from the size code, not measurements of a particular tire model.
How to Convert a Flotation Tire Size to Metric
The designation 35×12.50R17LT states a nominal diameter of 35 inches, a nominal section width of 12.50 inches, and a 17-inch wheel diameter. Those stated dimensions equal approximately 889 mm in diameter and 318 mm in width. The LT suffix identifies a light-truck flotation size.
To suggest metric size codes, the converter keeps the same wheel diameter and calculates combinations of metric section width and aspect ratio. It initially displays combinations within 2% of the flotation diameter and 5% of its width, sorted by the smallest absolute diameter difference, then width difference.
| Calculated metric suggestion | Nominal diameter | Nominal width | Difference from 35 × 12.50 in |
|---|---|---|---|
| 305/75R17 | 35.01 in | 12.01 in | Diameter +0.03%; width −3.94% |
| 325/70R17 | 34.91 in | 12.80 in | Diameter −0.25%; width +2.36% |
The first suggestion is closer in diameter; the second is closer in width. These are mathematical suggestions, not verified products or approved replacements. The 2% and 5% limits only filter the displayed results; they are not vehicle-fitment tolerances.
Metric vs. Flotation Tire Sizes
| Marking | Metric: 265/70R17 | Flotation: 35×12.50R17LT |
|---|---|---|
| First number | 265 mm nominal section width | 35 in nominal overall diameter |
| Second number | 70 aspect ratio | 12.50 in nominal section width |
| R | Radial construction | Radial construction |
| Number after R | 17 in nominal wheel diameter | 17 in nominal wheel diameter |
| LT, when present | LT prefix identifies LT-metric | LT suffix identifies light-truck flotation |
Section width measures across the tire’s sidewalls; it is not tread width. To browse calculated sizes by wheel diameter, see the Tire Size Chart.
If you already have two specific sizes and want to compare their dimensions, use the Tire Size Comparison Calculator.
Can You Use a Suggested Size on Your Vehicle?
A close numerical match does not establish fitment. This converter does not check whether a suggested size is sold, whether a specific tire has adequate load capacity, or whether it clears your vehicle.
- Start with the vehicle placard and owner’s manual. Check the specified tire size and whether front and rear sizes differ.
- Check the exact replacement tire. Compare its load index, speed rating, published dimensions, and approved rim-width range.
- Check wheel and vehicle compatibility. Confirm clearance and any vehicle-specific requirements with the relevant manufacturers or a qualified tire professional.
The U.S. Tire Manufacturers Association’s replacement guidance recommends the size, load index, and speed rating designated by the vehicle or tire manufacturer. It warns against choosing a smaller size or lower load-carrying capacity than originally specified.
Calculation Method and Accuracy
The converter uses 25.4 millimeters per inch. For a metric size:
- Sidewall height in millimeters = section width in millimeters × aspect ratio ÷ 100.
- Nominal diameter in inches = wheel diameter in inches + 2 × sidewall height in millimeters ÷ 25.4.
For a flotation size, the stated diameter and width are read directly in inches. Its calculated sidewall height is (nominal diameter − wheel diameter) ÷ 2.
For either format, nominal circumference = unrounded diameter × π. The tool estimates theoretical revolutions per mile = 63,360 ÷ unrounded circumference in inches. This is a geometry estimate, not a measured rolling-revolutions specification.
The tool keeps full precision for calculations. It displays inches and circumference to two decimal places, sidewall millimeters to one decimal place, diameter and width millimeters to the nearest whole number, and theoretical revolutions per mile to the nearest whole revolution.
Why might a published tire spec differ? A size designation provides nominal values. A particular tire model can have different published physical dimensions, and its section width depends in part on the measuring rim width. Tire Rack explains the limits of calculated tire dimensions. Use the exact tire model’s published specifications when physical clearance matters.
Conclusion
Use the tire size converter to turn metric or flotation markings into easy-to-read nominal dimensions and find nearby calculated size codes. Before choosing a replacement, check the exact tire’s published specifications and your vehicle’s requirements; a close numerical match alone does not establish fitment.
If you prefer to browse sizes in a table, use our Tire Size Conversion Chart to compare common metric and inch tire sizes.
Frequently Asked Questions
Is there an exact metric equivalent for an inch tire size?
Not necessarily. The converter lists close calculated dimensions, but it does not verify that a suggested size is manufactured or suitable for your vehicle.
Does 35×12.50R17LT always measure exactly 35 inches tall?
No. The 35 is the nominal diameter in the size designation. Check the exact tire model’s published overall diameter for a product-specific value.
Can a suggested metric tire fit my current wheels?
The tool keeps the same nominal wheel diameter, but it does not check the tire’s approved rim-width range, vehicle clearance, or load capacity. Verify those details for the exact tire and vehicle.
Does the converter assess load index or speed rating?
No. If an entered size includes a service description such as 102H, the tool can display it, but it does not decide whether that rating meets your vehicle’s requirements.
Why does the revolutions-per-mile result differ from a tire specification?
The result uses calculated nominal circumference. It does not measure a tire rolling under load. Use the published specification for the exact tire model when that value matters.
