Education
Stoichiometry Calculator
Last updated: May 31, 2026
Written by Blake Boege
A stoichiometry calculator is an educational chemistry tool used to compute quantitative relationships between reactants and products in a balanced chemical reaction. Based on the law of conservation of mass, the tool converts the starting mass of a reactant into moles using its molar mass, applies the stoichiometric coefficient ratio between the reactant and product, and converts the resulting product moles back into mass in grams. Chemistry students and researchers use this calculator to find theoretical yields, analyze reaction proportions, and verify chemical equations.
Estimate chemical reaction yields based on balanced equation coefficients. Convert reactants to moles, apply ratios, and calculate theoretical mass of products.
Quick Answer
Calculate reactant and product yields. Enter reactant amount, molar masses, and balanced equation coefficients to compute moles and theoretical product grams.
Common Reactions Presets
ESTIMATED PRODUCT QUANTITY
89.36 g
Yields 4.9603 mol of product from 4.9603 mol of reactant.
Step-by-Step Calculations:
- 1. Convert reactant mass to moles: 10 g / 2.016 g/mol = 4.9603 mol
- 2. Apply stoichiometric ratio: 4.9603 mol reactant × (2 / 2) = 4.9603 mol product
- 3. Convert product moles to mass: 4.9603 mol × 18.015 g/mol = 89.3601 g
Examples
10g H2 reacting to form H2O (2 H2 + O2 -> 2 H2O)
Reactant MM = 2.016 g/mol, coeff = 2 · Product MM = 18.015 g/mol, coeff = 2 · Product Yield = 89.36 grams H2O
44.1g C3H8 forming CO2 (C3H8 + 5 O2 -> 3 CO2 + 4 H2O)
Reactant MM = 44.1 g/mol, coeff = 1 · Product MM = 44.01 g/mol, coeff = 3 · Product Yield = 132.03 grams CO2
55.8g Fe forming Fe2O3 (4 Fe + 3 O2 -> 2 Fe2O3)
Reactant MM = 55.85 g/mol, coeff = 4 · Product MM = 159.69 g/mol, coeff = 2 · Product Yield = 79.77 grams Fe2O3
How it works
The calculator converts the reactant input mass into moles, scales it by the mole ratio (product coefficient / reactant coefficient), and then converts the product moles into final theoretical grams.
Stoichiometric Mass Yield Formula
Product Mass (g) = (Reactant Mass / Reactant MM) × (Product Coeff / Reactant Coeff) × Product MM
The Importance of Balanced Equations
Before performing any stoichiometry calculations, you must ensure your chemical equation is fully balanced. A balanced equation has equal numbers of atoms for each element on both the reactant side (left) and the product side (right). These coefficients reflect the conservation of mass and represent the relative mole proportions in which molecules interact.
Theoretical, Actual, and Percent Yield
Stoichiometry determines the theoretical yield of a reaction. In physical laboratory experiments, the actual yield is almost always lower than the theoretical maximum due to physical spillages, vaporizations, or reverse reactions. To measure the efficiency of a chemical synthesis, scientists calculate the percent yield:
Percent Yield = (Actual Yield / Theoretical Yield) × 100%
Related tools
Explore our other academic science and chemistry calculators, such as the Grams to Moles Calculator for direct molecular conversions, and the Limiting Reactant Calculator for multi-reactant mixtures.
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Frequently asked questions
Stoichiometry is the quantitative study of reactants and products in chemical reactions. It is based on the law of conservation of mass, which states that matter cannot be created or destroyed, meaning the amount of each element must balance on both sides of a chemical equation.
Calculating stoichiometry involves three main steps: 1) Convert your starting mass of reactant to moles (using its molar mass), 2) Apply the mole ratio from the balanced chemical equation coefficients to find the moles of the desired product, and 3) Convert the product moles back to mass (grams) using the product's molar mass.
A mole ratio is a conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction. The ratio is derived directly from the coefficients of the balanced chemical equation (e.g., in 2H₂ + O₂ → 2H₂O, the ratio of H₂ to H₂O is 2:2 or 1:1).
Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). You calculate it by summing the atomic weights of all the atoms in the chemical formula of the compound, which can be found on a standard periodic table.
A limiting reactant (or limiting reagent) is the substance that is completely consumed first in a chemical reaction, thereby limiting the maximum amount of product that can be formed. Any other reactants are considered to be in excess.
Theoretical yield is the maximum amount of product that can be generated from the given reactants under perfect conditions, which is what this calculator computes. Actual yield is the amount of product physically obtained from a real experiment, which is typically lower due to side reactions, transfer losses, or incomplete reactions.
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