Chemical Equation Balancer
Balance any chemical equation instantly and see the smallest whole-number coefficients, an element-by-element atom check, and the full step-by-step working.
Type an unbalanced equation using + and -> (or =), then get the balanced version instantly.
Balanced equation
CH4 + 2 O2 → CO2 + 2 H2O
Coefficients used: 1, 2, 1, 2
2
Reactant compounds
2
Product compounds
3
Elements involved
6
Sum of coefficients
Atom Balance Check
Confirm that every element has the same number of atoms on the reactant and product sides.
Step-by-Step Equation Balancing
Here's exactly how this answer was calculated, one step at a time.
Given: CH4 + O2 -> CO2 + H2O
Step 1: List every element that appears in the equation
These are the elements whose atom count must match on both sides once the equation is balanced.
C, H, OStep 2: Assign a coefficient to every compound
Give each compound an unknown multiplier — a coefficient — that will scale the whole formula up or down.
CH4, O2, CO2, H2OStep 3: Set up one balance equation per element
For every element, the total number of atoms coming from the reactants must equal the total number of atoms going into the products.
C: 1×CH4 = 1×CO2 | H: 4×CH4 = 2×H2O | O: 2×O2 = 2×CO2 + 1×H2OStep 4: Solve the system and reduce to the smallest whole numbers
Solving the linear system gives one valid ratio of coefficients; dividing through by their greatest common factor gives the smallest whole-number answer.
CH4 = 1, O2 = 2, CO2 = 1, H2O = 2Step 5: Verify the atom count on both sides
Every element now has exactly the same number of atoms on the reactant side as on the product side — the equation is balanced.
C: 1 = 1 ✓ | H: 4 = 4 ✓ | O: 4 = 4 ✓Step 6: Write the final balanced equation
CH4 + 2 O2 → CO2 + 2 H2O
Balanced equation:
CH4 + 2 O2 → CO2 + 2 H2O
Chemical Equation Balancer: Balance Any Equation Online
This chemical equation balancer takes any unbalanced chemical equation you type in and works out the smallest whole-number coefficients needed to balance it, instantly. Type something like CH4 + O2 -> CO2 + H2O and it returns the correct balanced version, along with an element-by-element atom check so you can see exactly why it's correct.
It's built for chemistry students, teachers grading homework, and anyone who needs a quick, reliable way to balance a reaction without doing the trial-and-error by hand. Every result comes with a full step-by-step breakdown, so you can either check your own answer or learn the method as you go. It also works for more advanced equations with several reactants and several products, not just the simple two-compound reactions most balancers stop at.
What Does It Mean to Balance a Chemical Equation?
A chemical equation describes a reaction: the substances you start with, called reactants, on the left, and the substances you end up with, called products, on the right. Balancing an equation means adjusting the number in front of each formula, called a coefficient, until the number of atoms of every single element is exactly the same on both sides.
This isn't optional — it's a direct consequence of the law of conservation of mass, which says matter can't be created or destroyed in an ordinary chemical reaction. Atoms don't vanish and they don't appear out of nowhere; they simply rearrange into new combinations, so however many atoms of hydrogen, oxygen, or any other element you start with, you must end up with exactly that same number.
How to Balance a Chemical Equation Step by Step
First, write down every element that appears anywhere in the equation. Second, count how many atoms of each element are in every single compound, reading the numbers straight from the chemical formula. Third, treat the coefficient in front of each compound as an unknown, and write one equation per element stating that the total atoms from the reactants must equal the total atoms in the products.
Fourth, solve that system of equations — by inspection for simple reactions, or algebraically for more complex ones — to find a ratio of whole numbers that works. Finally, divide all the coefficients by their greatest common factor so you're left with the smallest possible whole numbers. This calculator carries out every one of these steps internally and shows you the working underneath the result.
The Method This Calculator Uses
Simple equations can often be balanced by inspection — just adjusting coefficients by trial and error until both sides match. But equations with several elements and several compounds, especially redox reactions, quickly become difficult to balance this way, and trial and error can easily lead you to the wrong ratio or a much larger set of numbers than necessary.
This tool instead sets up the balancing problem as a system of linear equations, one equation per element, and solves it exactly using fraction arithmetic rather than rounded decimals. That means there's no risk of a rounding error sneaking into a large equation — the coefficients you get back are always exact, and always reduced to the smallest possible whole numbers.
Why Coefficients Matter, Not Subscripts
It's tempting, when an equation doesn't balance, to change the small numbers inside a formula, called subscripts — for example changing H2O to H2O2. This is a mistake, because a subscript defines what the substance actually is chemically. Change it and you've described a different compound entirely, hydrogen peroxide instead of water, not balanced the equation.
Coefficients, the numbers written in front of a formula, are the only numbers you're allowed to change when balancing. A coefficient just says how many molecules or formula units of that exact substance are involved — writing 2 H2O means two separate water molecules, each one still perfectly normal water.
Common Types of Reactions You Can Balance Here
Combustion reactions, where a fuel like methane or propane reacts with oxygen to form carbon dioxide and water, are some of the most common equations students are asked to balance, and this tool handles them instantly, including ones with several carbon and hydrogen atoms per molecule.
It also balances synthesis and decomposition reactions, double displacement (precipitation) reactions, acid-base neutralisation reactions, and more advanced redox equations with several reactants and products, such as reactions involving permanganate or dichromate ions. As long as the equation is written with correct chemical formulas, the underlying math works the same way regardless of reaction type.
Reading and Typing a Chemical Equation Correctly
Type each compound's formula using standard chemical notation — capital letters for the start of an element symbol, a lowercase letter if the symbol has two letters, and a number directly after an element for its subscript, with no spaces in between, like Ca(OH)2 or C6H12O6. Separate different compounds on the same side with a plus sign, and separate the reactant side from the product side with an arrow, written as ->, or with an equals sign.
You don't need to type in any coefficients yourself — leave every compound as its plain formula, and this calculator will work out the correct numbers in front of each one for you. If you do include a number by mistake, it's simply ignored, since the whole point of the tool is to calculate that number itself.
Common Mistakes When Balancing Equations
A very common mistake is balancing atoms one element at a time without checking that earlier elements are still balanced afterward — changing a coefficient to fix oxygen can easily throw hydrogen back out of balance. Working through every element carefully, and re-checking after each change, avoids this back-and-forth.
Another frequent error is stopping at a technically correct but not fully reduced answer — for example writing 4 H2 + 2 O2 -> 4 H2O, which does balance, but isn't in lowest terms. Every coefficient here shares a common factor of 2, so dividing through gives the simplest form: 2 H2 + O2 -> 2 H2O. Always divide every coefficient by their greatest common factor at the end so the equation is in its lowest whole-number terms, which this calculator does automatically every time.
Why Balanced Equations Matter in Real Chemistry
A balanced equation is the starting point for almost every stoichiometry calculation — working out how much product a reaction will make, how much reactant you need, or which reactant runs out first. Without a correctly balanced equation, every mole ratio calculated from it will be wrong, no matter how carefully the rest of the math is done.
This matters well beyond the classroom too. Industrial chemists use balanced equations to plan exactly how much raw material a production run needs; environmental scientists use them to calculate emissions from a combustion process; and pharmaceutical chemists use them to scale a lab-bench synthesis up to a full production batch, where even a small error in the ratio of reactants can be expensive or unsafe.
Balancing Redox and Multi-Compound Equations
Reactions with several reactants and several products — like the classic reaction between potassium permanganate and hydrochloric acid, which produces potassium chloride, manganese chloride, chlorine gas, and water all at once — are far harder to balance by trial and error, since changing one coefficient tends to unbalance several elements simultaneously.
This is exactly where a systematic method pays off. By setting up one equation per element and solving the whole system together, rather than one element at a time, this calculator finds the correct set of coefficients for these larger, more tangled equations just as reliably as it does for a simple two-reactant combustion reaction. It also works using exact fractions internally rather than decimal approximations, so even equations that need large coefficients — sixteen, for instance — come out exact, not rounded.
Worked Example: Balancing Propane Combustion
Start with the unbalanced equation C3H8 + O2 -> CO2 + H2O. Count the atoms in each formula: propane has 3 carbon and 8 hydrogen atoms, oxygen gas has 2 oxygen atoms, carbon dioxide has 1 carbon and 2 oxygen atoms, and water has 2 hydrogen and 1 oxygen atom. Balance carbon first: 3 carbons on the left needs 3 CO2 on the right. Balance hydrogen next: 8 hydrogens on the left needs 4 H2O on the right, since each water molecule only carries 2 hydrogens.
Now count total oxygen needed on the product side: 3 CO2 contributes 6 oxygen atoms, and 4 H2O contributes another 4, for 10 oxygen atoms altogether. Since O2 supplies oxygen two atoms at a time, that means 5 O2 molecules are needed on the reactant side. The final balanced equation is C3H8 + 5 O2 -> 3 CO2 + 4 H2O, and every element now matches exactly on both sides — which is exactly the answer this calculator returns instantly when you type in the unbalanced version.
Checking Your Own Answer Against This Calculator
If you've balanced an equation by hand and want to check it, type your own unbalanced version into this calculator and compare its answer to yours. If your coefficients are a multiple of the ones shown here — for example you wrote 4, 2, 4 where the calculator shows 2, 1, 2 — your answer is chemically correct but not in its simplest form, and should be reduced further.
If your coefficients don't match at all, look through the element-by-element atom check this calculator provides. It will show you exactly which element's atom count doesn't line up, which is usually far faster than re-checking an entire equation from scratch by trial and error.
Chemical Equation Balancer FAQ and Quick Reference
To balance a chemical equation, adjust the coefficients in front of each formula — never the subscripts inside a formula — until every element has the same total atom count on both sides. This is required by the law of conservation of mass.
This free online chemical equation balancer is built for homework help, exam revision, and everyday reaction-planning work. For regulated, safety-critical, or large-scale industrial use, always double check the balanced equation and every formula involved against a certified reference before relying on it for a real procedure.
Frequently Asked Questions
How do you balance a chemical equation?
Adjust the coefficient in front of each compound — never the subscripts inside the formula — until every element has the same number of atoms on the reactant and product sides.
Why can't I change the subscripts to balance an equation?
A subscript defines the compound itself. Changing it turns the substance into a different compound entirely, instead of balancing the original equation.
What symbol should I use to separate reactants and products?
Use -> or = between the reactant side and the product side, and + between compounds on the same side.
Why do balanced equations need whole-number coefficients?
Coefficients represent whole molecules or formula units reacting together, so the smallest whole-number ratio is the standard, simplest way to write a balanced equation.
What law explains why equations must be balanced?
The law of conservation of mass: atoms are rearranged in a chemical reaction, not created or destroyed, so the same number of each atom must appear on both sides.