Calculate reactant or product quantities from balanced chemical equations using mole ratios, with optional grams-to-moles and moles-to-grams conversions.
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Use mole ratios to convert a balanced equation into grams or moles Enter the known amount, its coefficient from the balanced equation, and the target coefficient. If either side is given in grams, add the matching molar mass and the calculator converts through moles first.
Calculation path
First convert any gram-based input to moles, then apply the coefficient ratio from the balanced equation, then convert to grams again if the target amount is requested in mass units.
Result
6 mol
2 mol; 2 mol × 3 / 1 = 6 mol
Known amount
2 mol
Known moles
2 mol
Mole ratio
3:1
Unknown amount
6 mol
Stoichiometric path The balanced equation fixes the mole ratio. This calculator does not balance equations or identify limiting reactants; it converts a known amount into the matching reactant or product amount from an already-balanced reaction.
Stoichiometry calculator for mole ratios, grams, and balanced equations
A stoichiometry calculator converts between reactants and products using the coefficients in a balanced chemical equation. Enter a known amount, choose whether it is in moles or grams, and the calculator applies the mole ratio to find the matching quantity on the other side of the reaction.
How stoichiometry works
Stoichiometry is the chemistry workflow that relates the amounts of reactants and products in a balanced equation. The coefficients in the equation tell you the mole ratio between substances, and that ratio is what lets a calculator move from one chemical amount to another.
For example, if the equation says 2H2 + O2 -> 2H2O, then 2 moles of hydrogen correspond to 2 moles of water. The ratio is 1:1 for H2 to H2O, even though the substances have very different molar masses.
unknown moles = known moles × (unknown coefficient / known coefficient)
Applies the balanced-equation ratio to move from one species to another.
grams = moles × molar mass
Converts the mole answer into a mass when the target amount is requested in grams.
Using grams and molar mass
If the known amount is given in grams, you must first convert that mass into moles using the substance's molar mass. Once the mole amount is known, the coefficient ratio gives the corresponding reactant or product amount.
If the result is also needed in grams, multiply the final mole amount by the target species' molar mass. That is why a stoichiometry calculator often needs one or two molar-mass inputs in addition to the balanced-equation coefficients.
Worked example: making water from hydrogen and oxygen
For the balanced equation 2H2 + O2 -> 2H2O, 4.0 moles of hydrogen correspond to 4.0 moles of water because the hydrogen and water coefficients are both 2. If you want the answer in grams, multiply 4.0 mol of water by water's molar mass of 18.015 g/mol to get 72.06 g.
If your hydrogen amount were entered as 8.064 g instead of 4.0 mol, the calculator would first convert 8.064 g by dividing by hydrogen's molar mass of 2.016 g/mol. That gives 4.0 mol, and the same coefficient ratio then leads to the same 72.06 g of water.
What this calculator does not do
This page does not balance chemical equations for you. The coefficients must already be correct before stoichiometric conversion starts.
It also does not choose a limiting reactant, calculate percent yield, or infer reaction completeness. Those are separate chemistry problems that need their own assumptions and, in some cases, additional data.
Stoichiometry is the part of chemistry that relates the amounts of reactants and products in a balanced chemical equation. It uses coefficients to convert from one species to another by mole ratio.
Do I need a balanced equation first?
Yes. The coefficients are the entire basis of the calculation, so the equation must already be balanced before you can convert between reactants and products.
How do I convert grams to moles first?
Divide the mass in grams by the substance's molar mass. That gives the number of moles, which you can then carry through the stoichiometric ratio.
Can this calculator solve for grams and moles?
Yes. If the known or unknown amount is entered in grams, the calculator uses molar mass to convert to or from moles as part of the stoichiometry step.
What is the mole ratio?
The mole ratio is the ratio of coefficients in the balanced equation. For 2H2 + O2 -> 2H2O, the ratio between hydrogen and water is 2:2, which simplifies to 1:1.
Is stoichiometry the same as limiting reactant?
No. Stoichiometry converts between substances using a balanced equation. Limiting-reactant analysis goes a step further and checks which reactant runs out first when more than one reactant amount is known.
What if the equation is not balanced?
The result will not be reliable. A stoichiometry calculator depends on accurate coefficients, so the equation should be balanced before you use it.
Can I use this for reactants and products?
Yes. The same mole-ratio logic works in either direction as long as the balanced equation is correct and the known amount is entered for one species.
Why does the calculator ask for molar mass?
Molar mass is only needed when the amount is entered or requested in grams. The mole ratio itself comes from the coefficients, but grams require a mole-to-mass conversion step.
When should I use a different calculator?
Use a molecular-weight calculator when you need molar mass first, a grams-to-moles or moles-to-grams converter when no reaction ratio is involved, and a percent-yield calculator when you want to compare actual and theoretical product.
