About TreadSize

What we do

Three free tools, all running entirely in your browser:

• Tire size decoder — type any metric or flotation tire size and instantly see every dimension: section width, sidewall height, overall diameter in inches and mm, circumference, and revolutions per mile.
• Side-by-side compare — compare a stock size to a candidate replacement. See the diameter difference percentage, speedometer error at 60 mph, ground clearance change, and a safe/caution/problematic fitment verdict.
• Plus sizing calculator — enter a base metric size and see safe +1 and +2 rim-inch options, each with the exact diameter delta so you can stay within the 3% rule.

Our approach

All calculations use standard ETRTO (European Tyre and Rim Technical Organisation) formulas — the same formulas used by tire engineers worldwide. There is no proprietary algorithm, no opinion injected into the math. The dimensions shown are what the formulas produce.

We do not store any data you enter. No tire sizes, no vehicle details, no search history. The tools run entirely client-side in your browser.

Independence

TreadSize is independently operated. We are not affiliated with any tire manufacturer, retailer, or automotive brand. When we eventually link to retailers (currently via an internal "where to buy" page), those links will be clearly disclosed as affiliate links. The math never changes based on who might earn a commission.

Data accuracy and limitations

Tire size math is deterministic — the formulas have been the same for decades. However, we strongly recommend confirming all fitment decisions with a qualified tire professional before purchasing. Actual dimensions vary slightly by manufacturer, rim width, and inflation pressure. What our tool shows is the computed nominal value, not a guaranteed measurement of any specific tire.

Contact

Questions or corrections: hello@treadsize.com