In the top row you need to select the size of the tires that are on your car at the moment. These indicators can be easily found on the sidewalls of your tires. In the first box you need to choose tire width in inches. The second box is for height and width ratio in percentages. The third field is for disc diameter in inches. In the second row you need to specify the size of the new tires, or the tires that you are going to buy. After you have entered all the parameters, click the green button "Calculate". Our tire size calculator uses inch measurements by default, but you can switch to metric system (cm) if you want.