How do you convert #2.16 x 10^6# into standard form?
The term "standard form" means different things to different people (in different parts of the world).
In many places "standard form" is a synonym for "scientific notation". This is what the other answer posted here assumes.
Also you may find "normal form" as another synonym for "scientific notation".
I expect what you were looking for is the answer given above:
but I don't know what term you could use for this form that would be universally accepted.
By the way before I get lots of comments that "standard form" is never used in the way (I assume) you meant, here is a link: