Stoichiometry Calculator: what this tool is for
The online stoichiometry calculator performs complete chemical reaction balance computations, unambiguously identifies the limiting reactant, and calculates maximum theoretical yields in both grams and moles.
Stoichiometry is grounded in Lavoisier's fundamental Law of Conservation of Mass: balanced reaction coefficients determine the exact molar proportions in which reactants combine and products form.
The calculator analyzes initial reactant quantities (in grams or moles), computes the maximum reaction progress x_max, identifies which reactant is exhausted first (limiting reagent), and quantifies remaining excess reactants.
It also allows you to compare theoretical maximum yield with your experimentally isolated product mass to determine the percent yield of your chemical synthesis.
A library of benchmark chemical reactions (methane combustion, Haber-Bosch ammonia synthesis, acid-base neutralization, calcium carbonate dissolution, iron oxidation) is included for instant calculation and educational verification.
No file stored
Nothing is saved on our servers, during or after processing.
Local processing
The computation runs in your browser whenever the technology allows it.
Instant result
No waiting and no export queue: the result appears live.
Free, no account
No sign-up, no daily limit and no intrusive ads.
What this tool gives you
Instant Limiting Reactant Identification
Unambiguously find which reagent limits reaction progress using automated stoichiometric ratio (n / ν) calculations.
Maximum Theoretical Yield Calculation
Obtain the exact maximum mass of product achievable assuming 100% complete chemical conversion.
Final State Reaction Table
Track initial, reacted, formed, and remaining moles and masses across all species in a structured reaction balance table.
Percent Yield Calculation
Enter your experimentally recovered product mass after purification to instantly compute your synthesis percent yield.
Real-world examples
Stoichiometric balance benchmarks for classic chemical reactions.
Combustion of 32 g of methane with 64 g of oxygen
The mixture contains 2 moles of CH4 (32 g / 16 g/mol) and 2 moles of O2 (64 g / 32 g/mol). Under CH4 + 2 O2 → CO2 + 2 H2O, 2 moles of CH4 require 4 moles of O2. Oxygen is limiting (x_max = 2/2 = 1 mol), forming 1 mol CO2 (44 g) and 2 mol H2O (36 g), leaving 1 mol CH4 (16 g) in excess.
Calculating percent yield for an aspirin synthesis
If a laboratory preparation has a theoretical yield of 10.0 g of acetylsalicylic acid and the chemist recovers 8.2 g of purified crystals, the percent yield is (8.2 / 10.0) × 100 = 82.0%.
How to use Stoichiometry Calculator
Select a reaction preset or customize
Pick a standard reaction from the list or set stoichiometric coefficients and chemical formulas for your reactants and products.
Enter initial reactant quantities
Specify the mass in grams (g) or amount of substance in moles (mol) for each starting reactant.
Identify limiting reactant and progress
The calculator computes max progress x_max, highlights the limiting reagent, and shows remaining excess reactant masses.
Calculate actual percent yield (optional)
Type the actual mass of product recovered from the bench to compute your experimental percent yield.
Tips and mistakes to avoid
Always balance your chemical equation first
Stoichiometry depends entirely on mass conservation. Ensure that atom counts for each element match on both sides of the arrow.
Compare molar ratios (n / ν), not raw masses
The limiting reactant is not necessarily the one with the smaller mass in grams, but the one with the smallest mole-to-coefficient ratio (n / ν).
Account for reactant purity
If using technical-grade reagents, calculate the net mass of pure compound before entering initial values into the stoichiometry balance.
Avoid : Comparing masses directly without converting to moles
Comparing 10 g of reactant A to 10 g of reactant B without dividing by molar mass leads to false identification of the limiting reactant.
Avoid : Forgetting stoichiometric coefficients in x_max
For a reactant with coefficient 2 (e.g., 2 O2), the maximum reaction progress is x = n(O2) / 2, not n(O2).
Frequently asked questions
Answers to the questions people ask about Stoichiometry Calculator.
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Updated on August 2026. See all tools