You would use kilograms (kg) to measure someone's mass in metric units.
The metric units used to measure mass are grams (g) and kilograms (kg).
The unit used to measure mass is the kilogram (kg) in the International System of Units (SI).
Units of measurement provide a standard to measure mass, length etc.So, it is useful.
It doesn't make sense to convert units that measure completely different things. You can only convert units of length to units of length, units of mass to units of mass, etc.
Grams
Tape measure
Units of measure are used to measure anything: length or volume, mass or speed, pressure or force etc.
Kilograms.
kilograms
You would use kilograms (kg) to measure someone's mass in metric units.
Grams
grams or other units
The international unit for mass is the kilogram.
AMU=Atomic Mass Unit
Scientists use atomic mass units (amu) or unified atomic mass units (u) to measure the mass of atoms and their subatomic particles. These units are based on the mass of a carbon-12 atom and are commonly used in the field of nuclear and particle physics.
The metric units used to measure mass are grams (g) and kilograms (kg).