A hand (or handbreadth) is a unit of length measurement, originally based on the breadth of a male human hand and now standardized at 4 inches (about 10 cm).
All metric units of linear measurement are multiples or sub-multiples of the meter. -- nanometer = 10-9 -- millimeter = 10-3 -- centimeter = 10-2 -- meter -- kilometer = 103 . . etc.