MJ Motor Factors tyresize calculator

The most common question from our customers is "what is the overall diameter of this tyre?". To make life a little easier we have provided a simple calculator and brief tutorial on tyre size calculation. Our online tyre size calculator will allow you to calculate the approximate diameter of a tyre for any given size.

Tyre size calculation basics
	Tyres are marked with a fairly standard set of size markings. For example (235/85R16). Referring to the above example size [235] This is the width in mm of the tyre from sidewall to sidewall when it's unstressed and you're looking at it head on (or top-down). This is known as the section width. Next [85], This is the ratio of the height of the tyre sidewall, (section height), expressed as a percentage of the width. It is known as the aspect ratio. In this case, 85% of 235mm is 199.75mm - the section height. The letter [R] in this case refers to the construction type RADIAL The final figure [16] is the rim diameter. This is the overall height of the actual wheel. To calculate the approximate overall diameter (height) of a tyre you need to do a little maths..... Height=section width/(aspect ration/100)*2+rim diameter in mm (not inches!) Rims are still usually calculated in inches (don't ask me they just are!). For you convenience we have created a simple calculator that you can use to take the headache out of calculating tyre height. Simply select the sizes from the menus and the diameter will be updated in the red boxes

Section width
Aspect ratio
Rim size
Overall height*	inches or mm

*Please note that the calculations provided by this page are approximate only. MJ Motor Factors accept no responsibility for accident, loss or damages of any kind howsoever caused as a direct or indirect result of using the information obtained from this website. Use of this calculator and website is at your own risk.