Stoichiometry Calculator
Calculate Stoichiometry values for science, physics, chemistry, and engineering problems.
This stoichiometry calculator uses a balanced chemical equation's mole ratios to find how much of a product forms, or how much of a reactant is needed, based on a given quantity of another substance in the reaction.
Enter the balanced equation, the known quantity of one substance, and the calculator returns the corresponding quantity of another substance.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 2H₂ + O₂ → 2H₂O: given 4 moles of H₂ | 4 mol H₂O produced | Mole ratio of H₂O to H₂ is 2:2 = 1:1. Moles H₂O = 4 × (2 ÷ 2) = 4 mol. |
| 2H₂ + O₂ → 2H₂O: given 3 moles of O₂ | 6 mol H₂O produced | Mole ratio of H₂O to O₂ is 2:1. Moles H₂O = 3 × (2 ÷ 1) = 6 mol. |
Mole Ratios from a Balanced Equation
The coefficients in a balanced chemical equation represent mole ratios between reactants and products. For 2H2 + O2 -> 2H2O, 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water - these ratios let you convert from moles of one substance to moles of any other substance in the reaction.
From Grams to Grams: The Full Stoichiometry Path
A typical stoichiometry problem converts grams of a known substance to moles (using its molar mass), then to moles of the target substance (using the mole ratio from the balanced equation), then back to grams (using the target's molar mass) - three conversion steps in sequence.
How to Use the Stoichiometry Calculator
- Open the Stoichiometry Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the stoichiometry calculator works.
Frequently Asked Questions
What is stoichiometry?
Stoichiometry is the calculation of quantitative relationships between reactants and products in a chemical reaction, based on the mole ratios given by a balanced chemical equation.
How do you convert grams to moles in a stoichiometry problem?
Divide the given mass by the substance's molar mass (grams per mole) to find the number of moles.
Why must the chemical equation be balanced first?
The mole ratios used in stoichiometry calculations come directly from the equation's coefficients - an unbalanced equation gives incorrect ratios and therefore incorrect calculated quantities.
How do I use this stoichiometry calculator?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the Stoichiometry Calculator calculate?
Calculate Stoichiometry values for science, physics, chemistry, and engineering problems. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this stoichiometry use?
The formula is: Moles B = Moles A × (Coefficient B ÷ Coefficient A). Stoichiometry rests on Lavoisier's law of conservation of mass (1789) combined with John Dalton's atomic theory (1803), which together established that chemical reactions rearrange atoms in fixed whole-number ratios rather than creating or destroying matter - the entire basis for why a balanced equation's coefficients can be trusted as exact mole ratios between reactants and products.
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Last updated: September 27, 2026.