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Stoichiometry Calculator

Balance chemical equations and calculate masses, moles, and volumes of reactants and products.

Stoichiometry Calculator

aA + bB → cC + dD

Enter an unbalanced chemical equation to balance it

Use + to separate compounds. Use -> or = or → as the arrow. Example: CH4 + O2 -> CO2 + H2O
Results update as you type.
n = mass / MW   |   mole ratio from coefficients

Enter a balanced equation, then specify a known amount to calculate the rest

Enter an already balanced equation with coefficients

How It Works

What is Stoichiometry?

Stoichiometry is the calculation of quantities of reactants and products in a chemical reaction. It uses the balanced equation and mole ratios to determine how much of each substance is consumed or produced.

Balancing Equations

A balanced chemical equation has equal numbers of each element on both sides. The calculator uses a matrix-based method (Gaussian elimination) to find the smallest whole-number coefficients.

2H₂ + O₂ → 2H₂O

Atoms balanced: H = 4, O = 2 on each side

Mass-Mole Conversions
  • Moles = mass / molecular weight — convert grams to moles
  • Mole ratio — from balanced equation coefficients
  • Mass = moles × molecular weight — convert moles back to grams
Step-by-Step Example

Problem: How many grams of H₂O are produced from 4 g of H₂?

Equation: 2H₂ + O₂ → 2H₂O

  1. Moles of H₂ = 4 g / 2.016 g/mol = 1.984 mol
  2. Mole ratio H₂ : H₂O = 2 : 2 = 1 : 1
  3. Moles of H₂O = 1.984 mol
  4. Mass of H₂O = 1.984 × 18.015 = 35.73 g
Supported Input Format
  • Element symbols with counts: H2O, CO2, Ca(OH)2, Fe2(SO4)3
  • Parentheses for polyatomic groups: Mg(OH)2, Al2(SO4)3
  • Separate compounds with +
  • Use ->, =, or → between reactants and products

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