Subscript Generator (H₂O, CO₂, x₁ — Unicode subscript numbers & letters)

Understanding the subscript generator — concept and principle

Subscripts appear below the line in chemical formulas (H₂O, CO₂) and indexed variables (x₁, aₙ). This generator writes them with Unicode subscript characters, so they survive in plain text. Its chemical-formula mode lowers only the atom counts and keeps coefficients full size, and an underscore mode lowers whatever follows "_".

How it is calculated

Unicode subscripts: digits ₀–₉ (U+2080–U+2089), signs ₊ ₋ ₌ ₍ ₎ and 17 letters (a, e, h, i, j, k, l, m, n, o, p, r, s, t, u, v, x); no capitals

Chemical mode: a digit is lowered only after a letter, a closing bracket or another lowered digit

Underscore mode: "_" is removed and the next number, letter, bracketed group or braced group is lowered

Everything mode: every character with a subscript form is lowered

Characters without a subscript form are counted.

The principle

In chemistry, numbers after an element symbol count atoms and are written as subscripts, while a number in front of a formula is a coefficient that counts molecules and stays full size. That is why "6O2" becomes 6O₂, not ₆O₂. The rule used here follows that convention: a digit is lowered only if it follows something that can carry a count. Unicode includes subscript digits and a limited set of subscript letters, mainly for phonetics, so only those can be lowered.

Worked example

Default inputs: "C6H12O6 + 6O2 → 6CO2 + 6H2O", chemical-formula mode.

1. C6 → C₆, H12 → H₁₂, O6 → O₆ (glucose).
2. 6O2 → 6O₂; the leading 6 is a coefficient and stays.
3. 6CO2 → 6CO₂ and 6H2O → 6H₂O.
4. Result: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O; characters lowered = 7; letters or digits without a form = 0.
5. UTF-16 length = 27.

How to read the result

Chemical mode is ideal for formulas and reaction equations, which follow IUPAC conventions for atom counts. Underscore mode suits maths and variables like x_1 or T_(max). Check charges and states separately: ion charges are usually written as superscripts.

Common mistakes

• Lowering coefficients in front of formulas.
• Expecting capital subscript letters; Unicode has none.
• Writing ion charges as subscripts instead of superscripts.
• Using Unicode subscripts in documents where real formatting is available and better.

Frequently asked questions

How do I write H₂O in plain text?

Use the subscript ₂ (U+2082), which this tool inserts in chemical mode.

Why isn't the 6 in 6CO₂ lowered?

It is a coefficient counting molecules, which is written full size.

Are there subscript capital letters?

No. Unicode has subscript forms for only 17 small letters.

How do I lower a group like "max"?

Use underscore mode with braces or brackets: T_{max} or T_(max).

Sources: The Unicode Standard 15.1, Superscripts and Subscripts block (U+2080–U+209C) and Phonetic Extensions (subscript letters) · IUPAC, Nomenclature of Inorganic Chemistry (Red Book, 2005), IR-4 (formulae)