Handy tyre size calculator

Use this tyre size calculator to calculate the diameter, width, sidewall, circumference, and revolutions per mile of any tyre. Just type in a metric or standard size tyre and click calculate. Inch measurement tyres are fairly easy to understand however metric tyres use a more difficult system to read. The first number on a metric tyre is the width. Divide this by 25.4 to get inch equivalent. The third number generally preceded by an "R" is the wheel diameter. The sidewall and aspect ratio are used in metric sized tyres to determine the overall height of a tyre. The second number on a metric tyre is to calculate the side wall measurement. The sidewall height is a percentage of the width of the tyre. This second number is that percent. The sidewall height or "aspect ratio" of a 285/75/R16 tyre is 75% of 285mm.