About

Size numbers are calculated by formula in your browser: sidewall height is section width × aspect ratio / 100, overall diameter is rim × 25.4 mm + 2 × sidewall, and revolutions per mile are 63,360 / (π × diameter in inches). These are nominal, unloaded numbers.

Measured numbers come from the tire makers’ own size tables on their official product pages: 28 tables from 5 makers (Nitto, Toyo, Kumho, Mickey Thompson, Firestone), each row stored with its address, the date it was read and the table row as printed. A size page is built only when the tables list at least 5 tires from at least 3 brands in that size. Rows whose published diameter is more than 4% off the formula are left out as likely table errors.

Load index and speed symbol tables use values confirmed by two published tire maker tables; values where makers’ tables disagree are not used. Rules are quoted from official texts: the Electronic Code of Federal Regulations (49 CFR) for the US and provincial government pages for Canada, each with the date checked.

The texts on this site are written by AI from saved facts: the formula results, the maker table rows and the quoted rules for each page. Code then checks every draft: each number must appear in those facts, rules must name their source, and drafts with fit promises, pressure advice or sales language are rejected. A page that fails the check is not published.

The site does not test tires and does not rate or rank them. It shows no prices, because tire prices change daily.

It does not tell you that a size fits your vehicle or that it is legal where you drive. Fit depends on the vehicle, wheels and suspension. For load and inflation pressure, use the tire and loading placard on the driver’s door jamb and the owner’s manual.

Some buttons lead to tire and wheel stores through addresses that start with /go/. If a store runs a partner program with this site and you buy after clicking, the site may earn a commission. It does not change the numbers on any page.

Corrections and questions: hello@tiresize.autos. If a maker updates a size table or a rule changes, write and the page will be rechecked.