Kilograms are the standard unit of mass in the metric system. Therefore, grams or milligrams can be used to get the mass of smaller objects.
The SI unit for mass is the kilogram (kg)
Triple-beam balances will find the mass of various objects!
A metric unit for measuring an objects mass is a gram and its multiples or submultiples such a decagram, centigram, milligram, hectogram, kilogram
Not sure what you mean with "light build". The SI (metric) unit for mass is the kilogram. For small objects, smaller units such as grams and milligrams can be used; for larger objects, the ton (= 1000 kilograms) is also used.
The currently official version of the metric system is called SI. The SI unit for mass is the kilogram. (In some older metric systems, the gram is the unit of mass.)