I think you guys are mixing apples and oranges here. That 72 DPI refers to MONITOR resolution. 72 DPI is a typical setting for a 19 inch monitor at 1024x768 screen resolution. It’s calculated by measuring the usable horizontal (or vertical) viewing area and dividing the measurement by the corresponding screen resolution.
Horizontal: 1024 / 14.2 = 72.11267606 … 72 DPI
Vertical: 768 / 10.6 = 72.4528301 … 72 DPI
All you need to be concerned about is the IMAGE resolution.
DPI = Dots Per Inch == Pixels Per Inch
Centimeters to Inches Conversion_Factor == 0.3937
Inches to Centimeters Conversion_Factor == 2.54
With that in mind, the rest is simple math.