Metric and Inch Tire Size Converter

How we calculate

Enter a complete metric size such as 225/50R17 or a flotation size such as 33x12.50R17. The converter shows width, outside diameter, rim diameter, and aspect ratio, together with a geometric description in the other notation. It accepts sizes supported by the site's existing parser and validation limits. It does not restrict results to a short list of common tire sizes or search a manufacturer's product catalog.

How we calculate: for a metric tire, sidewall height is width in millimeters times aspect ratio divided by 100. Outside diameter is twice that height plus the rim diameter converted to millimeters. Divide millimeters by 25.4 to obtain inches. For flotation input, width and outside diameter are already stated in inches. The equivalent aspect ratio is 100 times half the difference between outside and rim diameter, divided by width, with all lengths in the same unit.

A 33x12.50R17 label therefore describes a nominal width of 317.5 mm. Its sidewall height is eight inches and its calculated aspect ratio is 64 percent. The resulting 317.5/64R17 description expresses the geometry; it is not a catalog designation or an instruction to round to a nearby stocked size. A metric input can likewise produce an inch diameter that does not match the rounded flotation label sold by a tire maker.

No measuring-rim width correction is applied. Section width on a real tire is measured on a specified rim and can change on another permitted rim width. The label alone does not tell this tool that measuring-rim dimension or the manufacturer's approved rim range. Tread width, section width, load index, speed rating, and construction also describe different properties. The conversion retains the construction letter but does not establish equivalent load capacity or service suitability.

Use the dimensions as a starting point for reading specifications. Before buying a replacement, compare the particular models' published dimensions, load and speed requirements, and approved wheel range. The output is intentionally a nominal geometry comparison rather than a fitment match. Existing limits and unsupported legacy formats remain in place; an explanatory error is shown if an input cannot be evaluated. Use the comparison tool to inspect two proposed sizes side by side.

Frequently asked questions