Stoichiometry Calculator — Mole Ratio, Mass & Chemical Reaction CalculatorMoles = Mass / Molar Mass · Mole Ratio · Limiting Reagent · % Yield · Grams ↔ Moles
Use this free Stoichiometry Calculator to instantly calculate the mass of reactants or products in any balanced chemical equation using mole ratios and molar mass — following the standard stoichiometry calculation pathway: Step 1: Convert grams to moles (n = mass / molar mass) → Step 2: Apply mole ratio from balanced equation coefficients → Step 3: Convert moles back to grams (mass = n × molar mass) — delivering the theoretical mass of any reactant or product in seconds. Also calculates limiting reagent and excess reagent identification · theoretical yield in grams and moles · percentage yield (% yield = actual / theoretical × 100) — for complete reaction stoichiometry analysis.
This online stoichiometry calculator is trusted across all levels of chemistry education and chemical engineering practice: A-Level, AP Chemistry, IB Chemistry, JEE, and NEET stoichiometry exam problems, university general and organic chemistry coursework, laboratory reagent preparation and reaction planning, industrial chemical process mass balance calculations, pharmaceutical synthesis yield optimization, and environmental chemistry pollutant mass calculations. Mastering stoichiometry — the quantitative relationship between reactants and products in chemical reactions governed by the Law of Conservation of Mass and Avogadro's number (6.022 × 10²³ mol⁻¹) — is the foundational skill for all of analytical chemistry, synthetic chemistry, and chemical engineering.
⚠ Chemistry Disclaimer: This stoichiometry calculator assumes a perfectly balanced chemical equation and ideal reaction conditions (100% conversion). Real laboratory and industrial results will differ due to limiting reagent constraints, side reactions and by-product formation, incomplete reactions and equilibrium limitations, reagent purity and impurities, and practical yield losses during workup and purification. Always verify stoichiometric calculations against your balanced equation, molar mass data, and experimental conditionswith guidance from a qualified chemistry teacher, laboratory supervisor, or chemical engineer.
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Stoichiometry Calculator — Limiting Reagent, Theoretical Yield, and Percent Yield
Stoichiometry translates balanced chemical equations into quantitative predictions: given amounts of reactants, how much product forms? The key is the mole ratio from the balanced equation. For 2H₂ + O₂ → 2H₂O, the ratio is 2:1:2. Given 4 moles H₂ and 3 moles O₂, the stoichiometric requirement for 4 moles H₂ is 2 moles O₂ — but 3 moles are available. H₂ is the limiting reagent; the excess O₂ is 1 mole. The stoichiometry calculator identifies the limiting reagent and computes theoretical yield automatically from any combination of reactant masses.
Percent yield measures how close an actual reaction came to the theoretical maximum: %yield = (actual yield/theoretical yield) × 100%. A reaction with a theoretical yield of 10g that produces 7.8g has 78% yield. Yield below 100% is universal in real chemistry due to side reactions, incomplete conversion, product losses during workup, and measurement limitations. Yield above 100% indicates contamination, incomplete drying of product, or measurement error. The calculator sets up the theoretical yield so your experimental result can be immediately contextualized.
Multi-step synthesis stoichiometry compounds yield losses. A 5-step synthesis where each step is 85% efficient gives an overall yield of 0.85⁵ = 44.4% — less than half the starting material reaches the final product. This multiplicative nature of yield losses explains why route selection in pharmaceutical synthesis prioritizes yield at every step. The calculator chains multiple steps with individual yields to show the overall material consumption and efficiency of the complete synthetic route.