Stoichiometry Calculator

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.