Last updated: June 2026
Use this chemical equation balancer to find the smallest whole-number coefficients that conserve every element in a reaction. It is designed for O-Level, IGCSE, A-Level and Singapore H2 Chemistry students who want to see why an equation balances rather than simply memorising the answer.
- Enter the reactant formulae in the left-hand box, separated by plus signs.
- Enter the product formulae in the right-hand box.
- Do not enter the reaction arrow. The two boxes already show which side each substance belongs to.
- Parentheses, square brackets and optional state symbols such as (s), (l), (g) and (aq) are supported.
- Select Balance equation to see the coefficients, atom-balance equations and final atom-count check.
What is a chemical equation?
A chemical equation is a compact way of representing a reaction. Reactants appear on the left, products appear on the right, and an arrow shows the direction of chemical change.
This equation contains the correct substances, but it is not balanced because there are two oxygen atoms on the left and only one oxygen atom on the right.
What is a balanced chemical equation?
A balanced equation obeys the conservation of atoms. Atoms are not created or destroyed during an ordinary chemical reaction. They are rearranged into new combinations.
Both sides now contain four hydrogen atoms and two oxygen atoms. The equation is therefore balanced.
Coefficients and subscripts
A coefficient is written in front of a formula and tells us how many particles or moles are involved. A subscript is part of the chemical formula and tells us how many atoms of an element are present in one formula unit or molecule.
In 2H2O, the coefficient 2 applies to the entire water molecule. It represents four hydrogen atoms and two oxygen atoms altogether.
You may change coefficients when balancing an equation. You must not change H2O into H2O2, because water and hydrogen peroxide are different substances.
How to balance chemical equations
Start with correct chemical formulae. Count every element on both sides, then introduce coefficients until each element has matching totals. Finally, divide the coefficients by any common factor so that the smallest whole-number ratio remains.
For more complicated equations, each unknown coefficient can be represented by a letter. Conservation of each element then gives a set of simultaneous equations. This calculator uses that systematic method and displays the resulting atom-balance equations.
Worked examples
Example 1: Hydrogen and oxygen forming water
Put 2 in front of H2O to balance oxygen, then put 2 in front of H2 to balance hydrogen.
Example 2: Combustion of methane
Carbon is already balanced. Put 2 in front of H2O to balance hydrogen. The products then contain four oxygen atoms, so put 2 in front of O2.
Example 3: Aluminium reacting with oxygen
The lowest common multiple of 2 and 3 oxygen atoms is 6. Use 3O2 and 2Al2O3, then balance aluminium with 4Al.
Example 4: Neutralisation with brackets
Ca(OH)2 contains two hydroxide groups. Two HCl molecules are needed, producing two water molecules.
Common exam traps
Frequently Asked Questions
What does a chemical equation balancer do?
It finds coefficients that make the number of atoms of every element equal on the reactant and product sides.
Can I change subscripts when balancing equations?
No. Subscripts are part of the chemical identity of a substance. Only coefficients may be changed.
Why must equations be balanced?
Equations must obey conservation of atoms. The number of atoms of each element before the reaction must equal the number after the reaction.
Does this calculator support brackets?
Yes. It supports ordinary parentheses and square brackets in formulae such as Ca(OH)2 and K4[Fe(CN)6].
Does this calculator balance ionic half-equations?
No. This version balances atom counts in ordinary formula equations. Ionic charges, electrons, redox half-equations and waters of crystallisation require additional rules and are not supported here.