This tool lets you pick a standard school equation, type a whole-number coefficient for each substance, and then counts the atoms of every element on the left and right. If the counts differ, it tells you which element is out and by how much.
It trains the habit that matters most in balancing: count first, then change one coefficient, then count again. Subscripts stay fixed, so you cannot accidentally change the substance.
How do I use it?
- Choose an equation from the list, for example CH4 + O2 -> CO2 + H2O. Each substance gets its own coefficient box, all starting at 1.
- Type a whole number from 1 to 20 in each box. Leave a 1 where you want no visible coefficient.
- Press Count the atoms. You get the equation as you wrote it and a table with one row per element.
- Read the messages under the table, adjust one coefficient, and press the button again.
- Press Show the simplest balanced answer to compare with the smallest balanced set. Reset returns to the first equation.
Example walk-through
Start with H2 + O2 -> H2O, all coefficients 1. The table shows H: 2 on the left and 2 on the right, but O: 2 on the left and 1 on the right. The message says O has 2 atoms on the left but 1 on the right, so adjust a coefficient of a species containing O.
Put 2 in front of H2O. Now O matches (2 and 2), but H has become 2 on the left and 4 on the right.
Put 2 in front of H2 and the table shows H 4 and 4, O 2 and 2. The equation is 2H2 + O2 -> 2H2O, balanced in the simplest ratio.
Now try 4, 2, 4. The tool still marks it balanced, but notes it is not in the simplest ratio and shows you the divided version. Coefficients of 1 are hidden in the printed equation, which matches how you write it in an answer.
How do I read the result?
- Left side and right side columns: the total atoms of that element after multiplying by your coefficients.
- Balanced? column: Yes only when the two counts are equal for that element.
- Mismatch messages: they name the element, both counts and which way to adjust.
- Rule reminder: changing a subscript changes the substance, so only coefficients move.
What are the limits?
The equations come from an allowlisted list of everyday textbook examples. The tool balances atoms only. It does not check charge, states or whether a reaction would actually happen, and it gives no procedure for running any reaction.
The hint searches coefficients up to 12 and returns the smallest total. If you type a coefficient above 20 or a non-whole number, the tool asks you to correct it.
Which lessons explain the output?
Start with balancing atoms without changing subscripts, then practise checking a balanced equation independently. If you keep changing subscripts, read the clinic page on that habit.
Mixed questions are in the formulas and equations practice set. The wider collection is on the tools page.
Once your counting is steady, our team can work through larger equations with you. See online one-to-one Chemistry tuition for how that works.