To determine tire size, divide the size by 25.4 to convert it from inches to millimeters

https://canvas.instructure.com/eportfolios/3113141/tire_calculator_sizewrsh063/Recognizing_the_Basics_of_Tire_Sizing_StepbyStep_Guidelines_for_Making_Use_Of_a_Tire_Measurements_Calculator

To compute tire dimension, divide the diameter by 25.4 to transform it from inches to millimeters