The stoichiometry calculator uses mole ratios from a balanced chemical equation to find how many moles and grams of each substance react or form. Enter coefficients, molar masses, and a known quantity to solve the reaction.
Stoichiometry Calculator
| Substance | Coeff. | Molar Mass | Moles | Grams |
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How to Use the Stoichiometry Calculator
The stoichiometry calculator applies mole ratios from a balanced equation to find how much of each substance reacts or forms. This is the core skill in quantitative chemistry.
Step 1: Enter Coefficients and Molar Masses
For each substance in your balanced equation, enter the stoichiometric coefficient (from the balanced equation) and the molar mass (g/mol). Use the Molecular Weight Calculator if needed. For example, for 2H₂ + O₂ → 2H₂O: H₂ coeff=2, MW=2.016; O₂ coeff=1, MW=32.000; H₂O coeff=2, MW=18.015.
Step 2: Enter the Known Quantity
Select which substance you know, enter its amount, and choose moles or grams. The calculator converts grams to moles using molar mass if needed, then applies the mole ratio to every other substance.
Step 3: Read the Results
The table shows moles and grams for all substances. For a reaction problem, label reactants (negative) and products (positive) in your mind — the calculator gives absolute amounts based on the given quantity of one substance.
Limiting Reagent
To find the limiting reagent, run the calculator twice — once specifying the amount of each reactant. Whichever produces less product is the limiting reagent. The theoretical yield is the smaller of the two product amounts.
Frequently Asked Questions
What is stoichiometry?
Stoichiometry uses mole ratios from balanced equations to calculate quantities of reactants and products. If 2H₂ + O₂ → 2H₂O, the 2:1:2 mole ratio means 2 moles H₂ react with 1 mole O₂ to produce 2 moles H₂O. From 4 moles H₂, you'd produce 4 moles H₂O (using 2 moles O₂).
What is a limiting reagent?
The limiting reagent is the reactant that runs out first, stopping the reaction. To find it, calculate how much product each reactant would produce independently — the one that produces less is the limiting reagent. The other reactant is in excess. The theoretical yield is based on the limiting reagent.
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally. Nothing is transmitted.
What information do I need to use this calculator?
You need: (1) a balanced chemical equation with coefficients, (2) the molar masses of each reactant and product (use the molecular weight calculator), (3) the amount of one known substance in moles or grams. The calculator then finds moles and grams of all other substances.