Chemical Equation Balancer
Balance any chemical equation and check the atom count on both sides.
Use + between species and any arrow: ->, =, or →. States like (aq) and (s) are ignored, and existing coefficients are recalculated.
Balanced equation
2H₂ + O₂ → 2H₂O
Coefficients: 2 : 1 : 2
Check: atoms on each side
| Element | Reactants | Products | Balanced |
|---|---|---|---|
| H | 4 | 4 | ✓ |
| O | 2 | 2 | ✓ |
Molar masses
These are what turn a balanced equation into a mass calculation.
What balancing actually means
A chemical equation is a statement that atoms are conserved. Nothing is created and nothing disappears, so whatever goes in on the left has to come out on the right — rearranged, but all of it. Balancing is the bookkeeping that makes the equation say that honestly.
The only things you may change are the coefficients: the numbers written in front of each formula. A coefficient multiplies everything after it, so 2H2O means four hydrogen atoms and two oxygen atoms. Subscripts are part of the substance’s identity and are fixed.
Balancing by inspection, and where it runs out
For simple equations, inspection works: balance the element that appears in the fewest places first, leave oxygen and hydrogen until last because they turn up everywhere, and clear any fractions at the end by multiplying through. Combustion equations are the standard drill — balance carbon, then hydrogen, then oxygen last, and double everything if oxygen comes out as a half.
Inspection stops being practical when there are more than a handful of species, or when the same element appears in several compounds on the same side. The algebraic method used here does not care: each element becomes an equation, and the whole system is solved at once.
Reading the atom-count table
The table under the answer is the proof, and it is worth doing by hand at least once. Take each element, multiply its subscript by the coefficient of the species it is in, and add across each side. If a row does not match, the equation is not balanced — and if you are checking your own homework, the row that fails is the element you got wrong.
Next steps
A balanced equation is the input to nearly every quantitative chemistry problem. Once you have it, the stoichiometry calculator uses it to find the limiting reactant and the theoretical yield, and the molar mass calculator converts between grams and moles for each species.
Related Calculators
Frequently Asked Questions
How do you balance a chemical equation?
You choose coefficients — the numbers in front of each formula — so that every element has the same number of atoms on both sides. Subscripts inside a formula can never change: altering H₂O to H₂O₂ turns water into hydrogen peroxide. Only the coefficients move.
Why can I not change the subscripts?
Because the subscripts define what the substance is. Balancing is about how many of each substance react, not about what they are. If an equation will only balance when you change a subscript, then one of the formulas is wrong, not the coefficients.
What method does this use?
The equation is turned into a system of linear equations, one per element, and solved for the smallest whole-number solution. That is the algebraic method taught alongside trial-and-error, and unlike inspection it always terminates and always finds the smallest answer. The arithmetic is done in exact fractions rather than decimals, so no rounding can creep into the coefficients.
Can it balance redox and ionic equations?
Yes. Write the charges as Fe^2+, MnO4^- or Ca++ and the charge is treated as one more quantity that has to balance, alongside the elements. That is enough to balance net ionic equations such as Fe²⁺ + MnO₄⁻ + H⁺ → Fe³⁺ + Mn²⁺ + H₂O in one step, without splitting it into half-reactions.
Why does it say my equation cannot be balanced?
Almost always because an element appears on only one side — carbon in the reactants with no carbon-containing product, for instance — which means a species is missing. The error message names the element. The other cause is a mistyped formula: check subscripts first.
What does "this equation has more than one solution" mean?
It means what you wrote is really two independent reactions written as one, so there are infinitely many valid coefficient sets. C + O₂ → CO + CO₂ is the classic example: carbon burning to CO and carbon burning to CO₂ are separate reactions, and any mixture of them balances. Split them up if you need a single answer.
Do state symbols matter?
Not for balancing. (s), (l), (g) and (aq) describe the physical state and are ignored here, so you can paste an equation straight out of a textbook without stripping them.