Tire Size in Inches

The "in inches" conversion, and the sizes people actually search.

A metric tire size is stamped in millimetres and percent. The search "tire size in inches" is the conversion to overall diameter and section width. The calculator does any stamp. The pages below are the high-volume stamps already converted, because that is how the queries are written (275/65R20 in inches, 285/70R17 in inches).

The conversion

Section width in inches is the millimetre width divided by 25.4. Sidewall in inches is that width times the aspect ratio. Overall diameter is the rim plus two sidewalls. That is the whole trick. Flotation sizes skip it: the first number is already the diameter in inches.

A tire size converter is this same job with more examples. This page is the hub: conversion in one paragraph, then the sizes that earn the clicks.

High-volume sizes already converted

These are the stamps whose "in inches" searches were measured in the 2026-09-13 OpenSEO pull, largest first. Each link is a full converter page, not a row in a table.

Inches on the stamp are not always overall diameter

The 20 in 275/65R20 is the rim, not the tire. Overall diameter is 34.1 inches. Mixing those two numbers is the usual way a "20 inch tire" conversation goes wrong.

Frequently asked questions

How do I convert a tire size to inches?

Divide the millimetre width by 25.4. Multiply by the aspect ratio for the sidewall. Add the rim and twice the sidewall for overall diameter. Or use the calculator.

Is the last number the diameter in inches?

On a metric size, no: it is the rim. On a flotation size (33x12.50R15), yes: the first number is the overall diameter.