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Balanced-equation chemistry tool

Stoichiometry Calculator

Convert a known reactant or product quantity into a target quantity using coefficients, mole ratios, and molar masses.

Enter balanced-equation values

Solve a stoichiometry problem

Free tool
g

Given quantity of the known substance.

Coefficient before the known substance.

g/mol

Required when the known quantity uses grams.

Coefficient before the target substance.

g/mol

Required when the target result uses grams.

Use coefficients from a correctly balanced chemical equation. Molar mass is required for gram conversions.

Try an example:

Your result will appear here

Enter the known quantity and the two balanced-equation coefficients.

Chemistry overview

What is stoichiometry?

Stoichiometry uses a balanced chemical equation to calculate the quantitative relationship between reactants and products.

Equation coefficients provide mole ratios that connect a known substance with a target substance.

Formula

Stoichiometry mole-ratio formula

Target moles= known moles × (target coefficient ÷ known coefficient)

  • Known moles = known mass ÷ known molar mass
  • Target moles = known moles × mole ratio
  • Target mass = target moles × target molar mass

Calculation method

How to calculate stoichiometry

  1. Balance the chemical equation.
  2. Identify the known and target substances.
  3. Convert the known quantity to moles.
  4. Apply the coefficient ratio.
  5. Convert target moles to the requested unit.

Worked example

Convert hydrogen mass to water mass

For 2H₂ + O₂ → 2H₂O, calculate water produced from 4.032 g H₂.

  1. 4.032 ÷ 2.016 = 2 mol H₂
  2. 2 × (2 ÷ 2) = 2 mol H₂O
  3. 2 × 18.015 = 36.03 g H₂O

Balanced equations

Use coefficients as mole ratios

Enter the numbers written before chemical formulas. Do not use subscripts inside chemical formulas as coefficients.

In N₂ + 3H₂ → 2NH₃, the nitrogen-to-ammonia ratio is 2 ÷ 1.

Common errors

Common stoichiometry mistakes

  • Using an unbalanced equation.
  • Reversing the coefficient ratio.
  • Applying mole ratios directly to grams.
  • Entering an incorrect molar mass.
  • Rounding intermediate results too early.

Calculation limits

Assumptions and limitations

The equation must be correctly balanced, and all coefficients and molar masses must match the selected substances.

The result is theoretical and assumes complete reaction.

This calculator does not account for limiting reactants, excess reactants, percent yield, impurities, equilibrium, or experimental loss.

Supporting tools

Prepare your chemistry inputs

Find molar mass with the Molecular Weight Calculator, or convert grams and moles with the Mass to Moles Calculator.

Related calculators

Questions and answers

Stoichiometry calculator FAQ

What formula does the stoichiometry calculator use?

It converts the known quantity to moles, applies the target-to-known coefficient ratio, and converts target moles to grams when requested.

Why must the chemical equation be balanced?

Balanced coefficients provide the valid mole ratio between reactants and products.

When is molar mass required?

Molar mass is required whenever the known or target quantity is expressed in grams.

Can this solve grams-to-grams stoichiometry?

Yes. Enter the known mass, both coefficients, and both required molar masses.

Does this identify a limiting reactant?

No. Limiting-reactant calculations require the available quantities of multiple reactants.