Stoichiometry Calculator: Simple and Effective

What is Stoichiometry?

Stoichiometry is the calculation of quantities in chemical reactions. It allows you to determine how much product will form from given amounts of reactants, or how much reactant is needed to produce a desired amount of product. This calculator helps you perform these calculations quickly and accurately.

How to Use This Calculator

  1. Enter a balanced chemical equation using standard notation (e.g., 2H2 + O2 = 2H2O)
  2. Click "Parse Equation" to analyze the equation
  3. Select your known compound and enter its amount in grams
  4. Select the target compound you want to calculate
  5. Click "Calculate" to see the result

Enter Chemical Equation

Example equations you can try:

  • • 2H2 + O2 = 2H2O (Water formation)
  • • CH4 + 2O2 = CO2 + 2H2O (Methane combustion)
  • • 2Al + 3Cl2 = 2AlCl3 (Aluminum chloride formation)
  • • N2 + 3H2 = 2NH3 (Ammonia synthesis)

Understanding the Results

The calculator uses the following steps:

  1. Molar Mass Calculation: Determines the mass of one mole of each compound
  2. Mole Conversion: Converts the known mass to moles using molar mass
  3. Stoichiometric Ratio: Uses coefficients from the balanced equation to relate compounds
  4. Target Calculation: Converts moles of target compound back to grams

The three-step conversion behind every answer

Stoichiometry problems all boil down to the same chain: grams → moles → moles of a different compound → grams. You can't compare compounds directly by mass because they have different molar masses; converting through moles is what lets the balanced equation's coefficients (the ratio of how many molecules of each substance react) actually apply.

Worked example: methane combustion

Enter CH4 + 2O2 = CO2 + 2H2O and parse it. The calculator computes each molar mass from atomic weights: CH4 is 12.011 (C) + 4×1.008 (H) = 16.043 g/mol; CO2 is 12.011 + 2×15.999 = 44.009 g/mol; H2O is 2×1.008 + 15.999 = 18.015 g/mol.

Suppose you burn exactly 16.043 g of CH4 — conveniently, one mole. Step 1: moles of CH4 = 16.043 g ÷ 16.043 g/mol = 1.000000 mol. Step 2: the equation's coefficients give a 1:1 ratio between CH4 and CO2, so moles of CO2 = 1.000000 × (1/1) = 1.000000 mol. Step 3: mass of CO2 = 1.000000 mol × 44.009 g/mol = 44.009 g. The same 1 mole of CH4 also relates to water at a 1:2 ratio (1 CH4 makes 2 H2O), so that same combustion produces 2.000000 mol × 18.015 g/mol = 36.030 g of H2O.

Why the equation must already be balanced

The calculator reads coefficients directly from what you type — it doesn't verify or auto-balance the equation. If you enter an unbalanced equation like CH4 + O2 = CO2 + H2O (missing the 2s), the mole ratios it uses will be chemically wrong even though the tool will still produce a number. Balancing has to happen before the equation goes into the input field.

What the parser can and can't read

Formulas are parsed with a regex that matches capital-letter element symbols followed by an optional lowercase letter and an optional digit count (matching patterns like Ca, Cl2, or H2O), and it does not currently handle parentheses in formulas like Ca(OH)2 or hydrate notation. Stick to flat formulas without grouping parentheses for reliable parsing.