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Chemical equation balancer

Balances the equation and shows how. Handles brackets, polyatomic ions and hydrates, and prints an atom count for every element so you can check the result rather than trust it.

Write it as you would by hand. Use -> for the arrow and + between species. Brackets and hydrates both work: Al2(SO4)3, CuSO4·5H2O.

Try one

Working

  1. Elements involved: C, H, O. Unknowns: 4 coefficients.
  2. Write one conservation equation per element — atoms in must equal atoms out.
  3. Solve the system. 4 unknowns and 3 independent equations leaves one free variable, which is why coefficients are a ratio.
  4. Scale the ratio to the smallest whole numbers: 1 : 5 : 3 : 4.
  5. Check: every element now has equal atom counts on both sides.

Balanced equation

C3H8 + 5O2 → 3CO2 + 4H2O

Atom check

Atom counts on each side of the balanced equation
ElementLeftRight
C33
H88
O1010

Runs entirely in your browser — nothing is uploaded. Coefficients are solved over exact fractions rather than decimals, so ratios like 1:3 do not drift.

Short answer

How do you balance a chemical equation?

Balance the elements that appear in only one reactant and one product first, then work outward, leaving oxygen and hydrogen until last because they usually appear in several species. If a coefficient comes out fractional, multiply every coefficient through to clear it. Never change a subscript — that changes the substance rather than the quantity. Finish by counting every element on both sides, and add the states of matter.

Step by step

How to balance a chemical equation

  1. Type the unbalanced equation

    Brackets, polyatomic ions and hydrates are all handled — write the formula as it appears in your question, using -> or = between reactants and products.

  2. Read the element audit first

    The tool counts each element on both sides before balancing. If an element appears on only one side, a formula is wrong or a species is missing, and the audit names the element so you can find the typo.

  3. Balance in the right order

    Start with elements that appear in exactly one reactant and one product. Leave oxygen and hydrogen until last, because they usually appear in several species and balancing them early forces rework.

  4. Clear any fractions

    Fractional coefficients are normal in combustion equations. Multiply every coefficient through by the denominator to clear it — the balancer does this automatically and shows the ratio it started from.

  5. Add the states of matter

    (s), (l), (g) and (aq) are part of a correct equation, not decoration. Markers deduct for their absence, and they are the step most often forgotten once the numbers work.

Worked examples

Four equations, balanced with the working

Each of these was balanced by the tool above when this page was built, and each ends with an atom count on both sides — the check that actually proves an equation is balanced, and the one most often skipped.

Synthesis — hydrogen and oxygen: H2 + O2 -> H2O

  1. Elements involved: H, O. Unknowns: 3 coefficients.
  2. Write one conservation equation per element — atoms in must equal atoms out.
  3. Solve the system. 3 unknowns and 2 independent equations leaves one free variable, which is why coefficients are a ratio.
  4. Scale the ratio to the smallest whole numbers: 2 : 1 : 2.
  5. Check: every element now has equal atom counts on both sides.

Balanced2H2 + O2 → 2H2O

The classic fractional case: balancing oxygen first gives a coefficient of ½, which is then cleared by doubling every term.

Atom count either side of 2H2 + O2 → 2H2O
ElementReactant sideProduct sideBalanced
H44Yes
O22Yes

Combustion — methane: CH4 + O2 -> CO2 + H2O

  1. Elements involved: C, H, O. Unknowns: 4 coefficients.
  2. Write one conservation equation per element — atoms in must equal atoms out.
  3. Solve the system. 4 unknowns and 3 independent equations leaves one free variable, which is why coefficients are a ratio.
  4. Scale the ratio to the smallest whole numbers: 1 : 2 : 1 : 2.
  5. Check: every element now has equal atom counts on both sides.

BalancedCH4 + 2O2 → CO2 + 2H2O

Carbon and hydrogen appear in one species each, so they balance first. Oxygen is left until last because it appears in both products.

Atom count either side of CH4 + 2O2 → CO2 + 2H2O
ElementReactant sideProduct sideBalanced
C11Yes
H44Yes
O44Yes

Oxidation — iron to iron(III) oxide: Fe + O2 -> Fe2O3

  1. Elements involved: Fe, O. Unknowns: 3 coefficients.
  2. Write one conservation equation per element — atoms in must equal atoms out.
  3. Solve the system. 3 unknowns and 2 independent equations leaves one free variable, which is why coefficients are a ratio.
  4. Scale the ratio to the smallest whole numbers: 4 : 3 : 2.
  5. Check: every element now has equal atom counts on both sides.

Balanced4Fe + 3O2 → 2Fe2O3

Neither element balances in whole numbers on the first pass, which is normal for metal oxides. Multiply through at the end.

Atom count either side of 4Fe + 3O2 → 2Fe2O3
ElementReactant sideProduct sideBalanced
Fe44Yes
O66Yes

Neutralisation — with a polyatomic group: Ca(OH)2 + HCl -> CaCl2 + H2O

  1. Elements involved: Ca, Cl, H, O. Unknowns: 4 coefficients.
  2. Write one conservation equation per element — atoms in must equal atoms out.
  3. Solve the system. 4 unknowns and 3 independent equations leaves one free variable, which is why coefficients are a ratio.
  4. Scale the ratio to the smallest whole numbers: 1 : 2 : 1 : 2.
  5. Check: every element now has equal atom counts on both sides.

BalancedCa(OH)2 + 2HCl → CaCl2 + 2H2O

The bracketed hydroxide group is expanded before counting, which is why the subscript outside the bracket multiplies everything inside it.

Atom count either side of Ca(OH)2 + 2HCl → CaCl2 + 2H2O
ElementReactant sideProduct sideBalanced
Ca11Yes
Cl22Yes
H44Yes
O22Yes

Frequently asked questions

How do you balance a chemical equation?

Balance elements that appear in only one reactant and one product first, leave oxygen and hydrogen until last, and use a fraction temporarily if it helps, then multiply through to clear it. Always add the states of matter — markers deduct for their absence.

Why can't I change the subscripts?

Subscripts define the substance. Changing H2O to H2O2 does not balance the equation, it replaces water with hydrogen peroxide. Only the coefficients in front of a formula may change.

What if the coefficients come out as fractions?

That is normal in combustion equations. Multiply every coefficient through by the denominator to clear it — this balancer does that automatically and shows the ratio it started from.

Why does this equation say it cannot be balanced?

Usually because an element appears on only one side, which means a formula is wrong or a species is missing. The tool names the element so you can find the typo.