Three kinds of small
The page opens on small capitals, which sit on the baseline and read as an even, quiet line. Position switches to superscript, which floats the letters up, or subscript, which drops them below. Those two are the ones people mean by tiny text.
Swap the boxes to get ordinary text back. Type on the left and the result updates as you go.
These came out of phonetics, not typography
A typographer's small capitals are a second cut of a typeface. Unicode's are something else. ʀ is the symbol for a uvular trill in the International Phonetic Alphabet, ɴ a uvular nasal, ɢ a voiced uvular stop. Linguists needed a way to write those sounds, so the letters were encoded as the notation called for them, most of the set sitting together from U+1D00 in a block named Phonetic Extensions, with ʀ, ɴ and ɢ left behind at U+0280, U+0274 and U+0262 where the IPA had already put them.
Which means the set is whatever phoneticians happened to want. There is no small capital Q and no small capital X anywhere in Unicode. Q borrows ǫ, an o with a tail, and X stays lowercase.
F and S do exist, but they arrived late and from a different block, so they sometimes sit a shade differently from their neighbours depending on the font.
The gaps in the tiny letters are worse
Superscript and subscript were assembled the same haphazard way, for maths and phonetics rather than for decoration, and they're missing more.
There is no superscript q, one letter short of the 26. Subscript is thinner still and missing eight of them, so a word with a b or a g in it comes back part-shrunk and part-normal. No font can fix that, because the characters don't exist to draw.
Small capitals are the complete-looking option, and the reason this page starts there.
It loses your capitals
Small capitals have no case of their own. Every letter renders as a capital shape, so "Quiet" and "quiet" produce the same thing and the text comes back lowercase when you convert it.
Worth knowing before putting a name through it. As with everything in this family, a screen reader reads these as phonetic symbols rather than as the word, and search matches none of them.
Related conversions
Superscript is the same conversion with the raised letters given a page of their own, and a chart of exactly which ones exist. Bold goes the other way, for when small isn't the point.
Paste any of it into the Unicode converter to see which block each character came from.
Questions
What is the difference between small text and tiny text?
Nothing fixed. People use both for all three styles here: small capitals on the baseline, raised superscript and lowered subscript. This page does all three.
Why is one letter not small?
Because that character does not exist. There is no small capital X, no superscript q, and subscript is missing eight letters outright.
Why did my capitals disappear?
Small capitals have no uppercase and lowercase of their own. Everything folds to one set of shapes, and converting back gives lowercase.
Does small text work on Discord and Instagram?
In messages and bios, usually. Name fields are the ones that strip it, since they often normalise anything outside plain letters.