How this calculator works
List each reactant and product once and keep subscripts fixed. Exact rational elimination finds the unique positive integer ratio, then reduces it to its smallest whole numbers. Initial coefficients are ignored when balancing. Parentheses, square brackets and hydrate dots use the shared IUPAC formula parser. States are preserved. Optional caret charges add charge conservation. Equations with several independent balances or impossible species are rejected; balancing alone does not establish that a reaction occurs.
Formula
For every element, sum(reactant coefficient x atom count) = sum(product coefficient x atom count). Charged equations also conserve total charge.
Worked example
Fe + O2 -> Fe2O3 balances as 4 Fe + 3 O2 -> 2 Fe2O3. H2 + O2 -> H2O balances as 2 H2 + O2 -> 2 H2O.
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Frequently asked questions
Will changing subscripts help?
No. A subscript changes the compound. Only the coefficients are adjusted.
Can I enter hydrates?
Yes. Use a middle dot, as in CuSO4·5H2O, or a period.
Why is an equation rejected as ambiguous?
The listed species may permit more than one independent reaction, so atom conservation cannot choose a unique ratio.