About

TireSizeLab is a free tool for understanding tire size math: diameter, sidewall height, circumference, and speedometer error when upsizing.

All calculations are deterministic and done in-browser from the ISO metric tire formula. There's no login and no personal-data tracking — only aggregate page views via Plausible.

When you buy a tire through a link on this site, we may earn a commission. We don't sort by commission — listings are ranked by a composite of review score, review count, and stock status.