Tire size calculator

Decode a marking like 205/55R16 — diameter, circumference, sidewall — or compare a second size and see the speedometer error.

Formats: metric like 225/45R17, 195/65R15, or flotation like 31x10.50R15.

Everything runs in this browser.

How to use

  1. Enter the stock size, e.g. 205/55R16 or 31x10.5R15.
  2. Optionally add a second size to compare.
  3. Read the diameter, sidewall, and speed difference.

What it supports

Metric (205/55R16) and flotation (31x10.5R15) markings; width 125–355 mm, aspect 20–85, rim 10–30 in. Numbers are the size stamped on the sidewall — actual mounted diameter varies by brand and load.

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