About TireSize

TireSize is a free reference that turns any tire size such as 245/40R18 into its real dimensions — overall diameter, sidewall height, circumference, and revolutions per mile — all computed instantly in your browser.

We built it because fitment math is repetitive and easy to get wrong. Our pages are written and checked by automotive editors, and every number is calculated from the size itself rather than copied from a table that can drift out of date.

There are no accounts, no trackers, and nothing to install. Pick a size, read the specs, and compare plus-size or speedometer options.