Stoichiometry Calculator

Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer Last updated: August 20, 2026

📚 Confused about how this is calculated? Read the full The Mole Ratio: The One Bridge at the Heart of Stoichiometry →

A Balanced Equation Is a Recipe with Exact Proportions

Once an equation is balanced, its coefficients aren't just bookkeeping — they're an exact ratio for how much of each substance reacts and forms. Stoichiometry is the process of using that ratio to answer the practical question every synthesis eventually asks: starting from this much reactant, how much product should I expect?

The Formula

Mass of Product = (Moles of Reactant ÷ Coeff. Reactant) × Coeff. Product × Molar Mass of Product

The moles-to-coefficient ratio converts the reactant amount into "reaction units," which are then scaled by the product's own coefficient and converted to mass using its molar mass.

Where This Calculation Matters

Predicting theoretical yield — this calculation produces the theoretical yield used to evaluate percent yield after a reaction is run.
Scaling a reaction up or down — moving from a bench-scale test to a larger batch requires recalculating every reagent quantity proportionally.
Reagent purchasing — knowing how much product a given mass of starting material can produce informs how much reactant to buy.
Process cost estimation — stoichiometric yield calculations underpin raw material cost projections in manufacturing.

A Worked Example

For the balanced combustion CH4 + 2 O2 → CO2 + 2 H2O, starting from 16 g of methane (molar mass 16.043 g/mol, coefficient 1) to find the mass of CO2 produced (molar mass 44.009 g/mol, coefficient 1):

Moles of CH4 = 16 ÷ 16.043 = 0.9973 mol
Mass of CO2 = (0.9973 ÷ 1) × 1 × 44.009 = 43.891 g

How to Use This Calculator

Choose whether you're starting from a known mass or a known mole count of the reactant.
If starting from mass, enter Mass of Reactant (g) and Molar Mass of Reactant (g/mol); otherwise enter Moles of Reactant (mol) directly.
Enter the Stoichiometric Coefficient of Reactant and Stoichiometric Coefficient of Product from the balanced equation.
Enter the Molar Mass of Product (g/mol).
Select Calculate to get the mass of product formed.

Related Calculations

Need the balanced equation and its coefficients first? Start with the Chemical Equation Balancer. To find a compound's molar mass for use here, use the Molar Mass Calculator.

Principles of Chemical Stoichiometry and Theoretical Yield Calculations

A stoichiometry calculator computes mole-to-gram conversions, molar mass ratios, limiting reactants, theoretical product yields, and percent yields across chemical reactions. In industrial chemical synthesis and pharmaceutical manufacturing, stoichiometric modeling optimizes reagent usage and minimizes expensive chemical waste.

The Fundamental Stoichiometric Formulas

Moles (mol): n = Mass (g) / Molar Mass (g/mol)
Molecules / Atoms: N = n · N_A (Avogadro's Number: N_A = 6.02214 × 10²³ mol^-1)
Mole Ratio Conversion: Moles Product = Moles Reactant × [ Coefficient_Product / Coefficient_Reactant ]
Percent Yield (%) = [ ( Actual Experimental Yield ) / ( Theoretical Stoichiometric Yield ) ] × 100%

The Limiting Reagent Concept

The Limiting Reactant is the reagent that is completely consumed first in a chemical reaction, placing an absolute mathematical ceiling on maximum attainable product yield:

Calculate theoretical product yield for each starting reactant individually.
The reactant that produces the lowest theoretical yield of product is the Limiting Reactant.
All other starting reactants are classified as Excess Reactants.

Step-by-Step Worked Calculation Example

Example: Calculating Limiting Reagent and Theoretical Yield of Ammonia (NH₃)

Problem: Haber-Bosch reaction: N₂ + 3 H₂ → 2 NH₃. Starting with 28.0 g of N₂ (Molar Mass = 28.02 g/mol) and 9.0 g of H₂ (Molar Mass = 2.016 g/mol). Ammonia Molar Mass = 17.03 g/mol. Calculate: (1) Initial moles of each reactant; (2) Identify the limiting reactant; (3) Theoretical yield of NH₃ in grams; and (4) Percent yield if 25.5 g of NH₃ is collected experimentally.

Step 1: Calculate Moles of Starting Reactants:

Moles N₂ = 28.0 g / 28.02 g/mol = 0.9993 mol N₂

Moles H₂ = 9.0 g / 2.016 g/mol = 4.4643 mol H₂

Step 2: Determine Theoretical Yield from each reactant:

From N₂: 0.9993 mol N₂ × ( 2 mol NH₃ / 1 mol N₂ ) = 1.9986 mol NH₃

From H₂: 4.4643 mol H₂ × ( 2 mol NH₃ / 3 mol H₂ ) = 2.9762 mol NH₃

Because N₂ yields fewer moles (1.9986 mol vs 2.9762 mol), N₂ is the Limiting Reactant.

Step 3: Calculate Theoretical Yield in Grams:

Theoretical Yield = 1.9986 mol × 17.031 g/mol = 34.04 Grams of NH₃

Step 4: Compute Percent Yield:

Percent Yield = ( 25.5 g / 34.04 g ) × 100% = 74.91% Percent Yield

Conclusion: The reaction produces 34.04 g theoretical yield with a 74.9% experimental efficiency.

Gas Stoichiometry at Standard Temperature and Pressure (STP)

For chemical reactions involving gaseous reactants or products (such as combustion or gas evolution reactions), chemical engineers utilize the Ideal Gas Law (P·V = n·R·T):

At STP (0°C / 273.15 K and 1.0 atm): 1.000 Mole of Any Ideal Gas = 22.414 Liters (Molar Volume)
Gas Volume (L) = Moles (n) × 22.414 L/mol

Solution Stoichiometry and Volumetric Titrations

In analytical aqueous chemistry:

Molarity (M) = Moles of Solute (n) / Volume of Solution (L)
Volumetric Acid-Base Titration Equivalence: M_acid · V_acid · n_H+ = M_base · V_base · n_OH-

Atom Economy and Green Chemistry Metrics

In sustainable pharmaceutical manufacturing, chemical engineers evaluate reaction efficiency using Percent Atom Economy:

Percent Atom Economy (%) = [ ( Molar Mass of Desired Product ) / ( Total Molar Mass of All Starting Reactants ) ] × 100%

While percent yield measures experimental recovery efficiency, atom economy measures intrinsic synthetic elegance — high atom economy reactions (such as addition and rearrangement reactions) incorporate 100% of reactant atoms into the desired final pharmaceutical product without generating toxic waste byproducts.

Consecutive Multi-Step Reaction Stoichiometry

In complex industrial synthesis (such as the multi-step synthetic pathway for acetaminophen or ibuprofen):

The product of Reaction 1 serves as the starting reagent for Reaction 2. Chemical process engineers compute Overall Process Yield by multiplying individual stage fractional yields:

Overall Multi-Step Yield = Yield_{Step 1} × Yield_{Step 2} × Yield_{Step 3} × ... × Yield_{Step N}
For a 5-step synthesis where each step achieves 90% yield: Overall Yield = ( 0.90 )⁵ = 59.05%!

Hydrate Stoichiometry and Empirical Formula Determination

Many inorganic crystalline salts incorporate water molecules within their solid crystal lattice (hydrated crystals, such as copper(II) sulfate pentahydrate: CuSO₄·5H₂O).

Stoichiometric gravimetric analysis heating a hydrated sample to evaporate water allows chemists to calculate the precise molar ratio of anhydrous salt to crystal water molecules, determining the salt's empirical formula.

Combustion Elemental Microanalysis

Analytical chemistry laboratories determine the empirical formulas of unknown organic pharmaceutical compounds by burning milligram samples in pure oxygen, measuring mass outputs of CO₂ and H₂O gas absorbers to calculate exact elemental carbon, hydrogen, and oxygen stoichiometric percentages.

Gravimetric Analysis in Quantitative Chemistry

Analytical chemists precipitate insoluble compounds (e.g., adding silver nitrate to precipitate silver chloride), filter, dry, and weigh the precipitate to determine unknown ion concentrations.

Excess Reagent Leftover Calculations

Subtracting the stoichiometric moles of excess reactant consumed from the initial starting moles determines the exact unreacted excess reagent mass remaining.