Many automotive websites provide tire sizes in inches, including Tire-Size-Conversion.com, DiscountTire.com, and PowerDog.com. Most sites also have tires listed for purchase that meet required measurements. With Tire-Size-Conversion.com, users can also convert metric tire sizes into inches and inches into metric units.
When calculating tire size, users should note the tire type, width, aspect ratio, construction and diameter. Tire measurements usually come in a string of numbers and letters that represent each quality. For example, P215/65R15. In this case, P is the type, 215 is the width, 65 is the aspect ratio, R is the construction, and 15 is the wheel diameter.