The formula this page uses
atoms of each element on the left = atoms of the same element on the right
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Balancing Equations Chemistry Calculator
Solve balancing equations chemistry problems with clear steps, notation, and a final check.
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Calculate without using AI.
Evaluate the governing formula locally in your browser. Define each known quantity once, then change values to test another case instantly.
Choose an example or enter a formula.
Show your work Step-by-step method
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Science
Balancing Equations Chemistry Calculator explained
The short version
- Balancing means making every element's atom count match on both sides of the arrow.
- You may change the big numbers in front, called coefficients. You may never change the small subscripts.
- Leave oxygen and hydrogen until last, because they usually appear in more than one compound.
What each part means
SymbolWhat it means
coefficient — The number in frontHow many units of that whole formula take part. This is the only number you are allowed to change.
subscript — The small number insideHow many atoms are in one molecule. Changing it makes a different substance.
reactants — Left of the arrowThe starting materials.
products — Right of the arrowWhat the reaction makes.
Show your work: a full example
- The unbalanced equationC₃H₈ + O₂ → CO₂ + H₂O
- Balance carbon first3 C on the left, so 3 CO₂ on the right
- Balance hydrogen next8 H on the left, and each H₂O holds 2, so 4 H₂O
- Now count oxygen on the right3 CO₂ gives 6 O and 4 H₂O gives 4 O, so 10 O in total
- Each O₂ supplies 2 atoms10 ÷ 2 = 5, so 5 O₂ on the left
- The balanced equationC₃H₈ + 5O₂ → 3CO₂ + 4H₂O
- Final countleft: 3 C, 8 H, 10 O. right: 3 C, 8 H, 6 + 4 = 10 O ✓
A second, different case
- A different case: a fraction appearsFe + O₂ → Fe₂O₃
- Balance iron2 Fe on the right, so 2Fe + O₂ → Fe₂O₃
- Count oxygen3 on the right, and O₂ supplies 2 at a time
- A fraction fixes it2Fe + 3/2 O₂ → Fe₂O₃
- Coefficients must be whole numbersmultiply every coefficient by 2
- The balanced equation4Fe + 3O₂ → 2Fe₂O₃
- Final countleft: 4 Fe, 6 O. right: 4 Fe, 2 × 3 = 6 O ✓
Copy-ready example
C₃H₈ + O₂ → CO₂ + H₂O
The unbalanced equation
Questions about the Balancing Equations Chemistry Calculator
Why can I never change a subscript?
Because the subscripts define the substance. H₂O and H₂O₂ are water and hydrogen peroxide, two chemicals with different properties. Coefficients only say how many units react, which is a free choice.
Which element should I balance first?
Start with the element that appears in the fewest formulas, usually a metal or the carbon in an organic compound. Save oxygen and hydrogen for last because they turn up almost everywhere.
Are fractional coefficients ever acceptable?
In thermochemistry, yes. Writing H₂ + ½O₂ → H₂O is standard when you want the enthalpy per mole of water. For an ordinary balancing question, clear the fraction.
What if an equation simply will not balance?
Check the formulas first, because a wrong one is the usual cause: writing NaCl₂ instead of NaCl makes balancing impossible. For redox reactions in solution you may also need to add H⁺, OH⁻ or H₂O and balance charge as well as atoms.