View Here : Tire Size Comparison
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.
Tire Sizing Example Using a 110/100-18 Rear Tire Using a common 110/100-18 rear tire as an example; the first number, 110, indicates the width of the tire in millimeters. The second number,100, is the aspect ratio, which is the height of the sidewall in relation to the width of the tread (100% of 110mm).