That depends what aspect of the adult you want to measure: the adult's height, mass, weight, volume, albedo, intelligence (no SI unit for that!), etc.
The metric unit of length is the 'meter'.
Any metric measure of volume.
The Newton
The metric unit is the meter scaled to centimeters.
Weighing balance is used to measure mass. The metric unit is kilograms.
The SI unit for mass in the metric system is the kilogram.
metre
second
The metric system
The metric unit used is feet and inches. centimeter can also be used
in feet
grams