View Here : Tire Size Comparison
Tire width is the maximum width of the tire which is usually at the sidewall of an inflated tire. Tread width is the actual width of the tire tread (which is normally less than the tire width). An "LT" after the tire size indicates that the tire is designed for "Light Truck" use.
Deere and Company offers a tire size conversion chart that compares tire inch size to its metric equivalent in millimeters. For instance, an 11.4 inch tire is the same as a 290 millimeter tire. The chart also shows the formulas for doing the conversions mathematically.