Tire Size Calculator — Compare Tire Dimensions

Parse metric tire codes (205/55R16) into real dimensions and compare two sizes including speedometer error.

Enter a size like 205/55R16 to see dimensions.

How this conversion works. Dimensions follow the standard metric tire designation (width mm / aspect % R rim inches) defined in ISO 4000-1 (passenger car tyre designation).

How to use

  1. Type a tire code such as 205/55R16 (a second tire is optional).
  2. Read width, sidewall, diameter, and circumference for each.
  3. Compare diameter difference and speedometer error between the two.

Frequently asked questions

What does 205/55R16 mean?

205 = section width in mm, 55 = aspect ratio (sidewall is 55% of width), R = radial construction, 16 = wheel diameter in inches. Total diameter = 16×25.4 + 2×(205×0.55) mm.

How is speedometer error calculated?

Speedometers count wheel revolutions. With a new diameter D2, actual speed = indicated × D2/D1 — a 3% larger tire means you travel 3% faster than the gauge shows.

How much size difference is acceptable?

A common rule of thumb keeps the overall diameter within ±3% of stock to protect speedometer accuracy, gearing, and ABS calibration. Check your vehicle documentation.

Is my data sent to a server?

No. Parsing and comparison run entirely in your browser.

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