International System of Units

I state that I hate abbreviations.
Force me to understand what they're talking about.
That's why the title of this post is not SI, how often do you find (which might be Sintax index, or a thousand other things ...).

Typing in any search engine "International System of Units summary” are given enough information to properly write the units of any size.

For those unwilling to make the effort to look for them, some links (with my comments):

very clear
SI Brochure 8th edition,
elabotaded by Comité International des Poids et
Mesures (CIPM).