Why copy subscript instead of formatting it
A small 2 made with a word processor's subscript button is formatting: paste it into a chat, a spreadsheet cell or a social post and it turns back into a full-size 2. The characters from this page are lowered digits in their own right (₂ is its own character, not a styled 2), so H₂O stays H₂O wherever it lands.
Chemical formulas convert completely
All ten digits have a subscript (₀₁₂₃₄₅₆₇₈₉). In Formula mode only the numbers that follow a letter or a bracket become subscript, so 6CO2 + 6H2O comes out as 6CO₂ + 6H₂O: the coefficients stay full size and letters such as the a in NaCl are never touched. Whole text lowers every character that has a subscript form.
Subscript letters are limited
Unicode has subscript forms for only 17 lowercase letters: a e h i j k l m n o p r s t u v x. There is no subscript b c d f g q w y z, and no capital letter has a subscript at all. Missing characters stay normal and the generator lists them, so you know what you are pasting.
Every subscript character
Tap a character to copy just that one, for example to fix a single number in a formula you already typed.
Lowered digits and signs
The 17 subscript letters
Greek letters
In Word and documents, use formatting instead
Writing a lab report or chemistry homework? There, the subscript button covers every letter, capitals included. The Word shortcut is Ctrl and the Equal sign (=) on Windows, Control and Equal on a Mac, no Shift; Ctrl and Spacebar clears it (Microsoft support).
Charges such as ²⁻ go up, not down: get them from the superscript generator.
Source of the subscript set: the <sub> decompositions in Unicode 13.0.0. The conversion runs on your device only.
Questions
How do I type subscript on a keyboard?
There is no subscript key on any standard keyboard. Paste-ready subscript comes from this page; inside Word or Google Docs, the shortcut is Ctrl and the Equal sign (=).
How do I write H2O with a small 2?
Type H2O in the box above with Formula mode on and copy H₂O. All digits have a subscript form, so any chemical formula works.
Why are some letters not converted?
Unicode only has subscript forms for 17 lowercase letters and none for capitals. The others stay normal, and the generator lists them.