Subscript and superscript are opposites by definition — subscript sits below the baseline, superscript sits above it — but the confusion usually isn't about direction, it's about which one to reach for. The short version: superscript is for footnotes, exponents, and ordinal suffixes; subscript is for chemical formulas and indexed variables. Both are available as instant copy-paste Unicode through the subscript generator and superscript generator on this site.
What each one looks like
Superscript raises characters above the normal line, the way an exponent sits above a number: x² or a footnote marker¹. Subscript lowers them below the line, the way the 2 sits in H₂O. Both are implemented in Unicode as separate character blocks rather than a formatting toggle — that's a deliberate design choice covered in more depth in Unicode Explained.
Where each is actually used
Superscript: mathematical exponents (x³), footnote and citation markers, ordinal indicators (1ˢᵗ, 2ⁿᵈ), and trademark/copyright-style marks. Subscript: chemical formulas (H₂O, CO₂), mathematical subscripted variables (xₙ, aᵢ), and some phonetic notation.
Which one has better Unicode coverage
This is the detail most guides skip: Unicode's superscript Latin letters are close to a complete alphabet, so a superscript generator can convert almost any word cleanly. Subscript is noticeably less complete — Unicode only defines subscript forms for a subset of lowercase letters (a, e, o, x, and a handful of consonants), so a subscript generator has to leave some letters unchanged. Numbers are the exception: both subscript and superscript digits (0–9) are fully defined in Unicode, which is why chemical formulas like H₂O convert perfectly even though a full subscripted sentence wouldn't. More detail on that in our chemistry-formula guide.