Chemical Equation Balancer
Type an unbalanced chemical equation and this calculator works out the smallest whole-number coefficients that balance every element.
Separate reactants and products with -> or =, and separate formulas with +, e.g. H2 + O2 -> H2O.
How to balance a chemical equation by hand
- List how many atoms of each element are on the reactant side and the product side.
- Start with the element that appears in the fewest formulas, and add a coefficient to even it up.
- Balance one element at a time, leaving oxygen and hydrogen until last (they often appear in the most formulas).
- Check every element again, and reduce the coefficients to the smallest whole numbers if they share a common factor.
Worked example: methane burning
CH₄ + O₂ → CO₂ + H₂O is unbalanced: the left has 4 hydrogens and 2 oxygens, the right has 2 hydrogens and 3 oxygens. Putting a 2 in front of H₂O balances hydrogen (4 and 4), then a 2 in front of O₂ balances oxygen (4 and 4), giving CH₄ + 2O₂ → CO₂ + 2H₂O.
Balance equations on a 3D scale and watch the molecules rebuild as products in Balancing Equations below.
Frequently asked questions
Why do chemical equations need to be balanced?
The law of conservation of mass: atoms are never created or destroyed in a chemical reaction, so the same number of each element must appear on both sides of the equation.
What are coefficients in a balanced equation?
The numbers placed in front of a formula to show how many units of it react or form, e.g. the 2 in 2H₂O. A formula with no number in front has a coefficient of 1.
Can you change the subscripts to balance an equation?
No — subscripts are fixed by the formula of the substance (H₂O is always 2 hydrogens and 1 oxygen). Only the coefficients in front of each formula can be changed.
How do you balance Fe + O2 → Fe2O3?
Balance oxygen and iron together: 4Fe + 3O₂ → 2Fe₂O₃ gives 4 iron and 6 oxygen atoms on both sides.
