The SI unit is the standard system of measurement used to help scientist to compare data and communicate with each other about with their results.
There is only ONE defined unit for mass in the SI, the kilogram. Other variants are commonly used for convenience, the gram and the tonne, but the kg is the base unit. Check out SI with your favourite search engine.
SI is an abbreviation of the French "le Système International d'unités"which when translated in to English means "The International System of Units".
There are 7 basic units
Watts
a specific combination of base units with its own name
In SI units, that would be the Newton.In SI units, that would be the Newton.In SI units, that would be the Newton.In SI units, that would be the Newton.
Derived SI units.
SI and metric are the same units.
International System of Units (SI)
Base units
most of the world does SI so more people can understand with it in SI units
most of the world does SI so more people can understand with it in SI units
SI units are more accurate than English system units
The standard SI unit for mass is the kilogram, or the gram. Smaller units may be used if necessary, such as the milligram.
The SI has 7 base units. These units can be combined in an almost unlimited way to form other (derived) units. The Wikipedia article on "SI derived units" lists some examples.
Si and metric are the same thing. SI was a redefinition of metric in 1960.
SI units: kilogram, gram English units: pound-mass, slug