Stoichiometry Calculator

Need to figure out how much product forms from a reaction? Our Stoichiometry Calculator makes it easy — just enter your balanced equation, select the known and target species, and instantly convert between moles, grams, and particles with step-by-step guidance.

Background

Stoichiometry relates the amounts of reactants and products using the coefficients of a balanced chemical equation. This calculator converts a known quantity (moles, mass, or particles) of one species into the corresponding quantity of another species by applying the mole ratio from the balanced equation. Enter a balanced equation, choose the known and target species, specify the known amount type and value, and get the target amount with a clear step-by-step result.

In simple words, stoichiometry is the “recipe” of chemistry—it tells you how much of each ingredient (reactant) you need and how much product you’ll get. Whether you are converting between grams, moles, or even number of molecules, the method always relies on the balanced chemical equation.

Enter values to calculate stoichiometry:

Balanced Equation:

Known Quantity Type:

Moles

Mass (g)

Particles

Known Species:

Target Species:

Known Value:

Molar Mass of Known (g/mol):

Target Quantity Type:

Moles

Mass (g)

Particles

Molar Mass of Target (g/mol):

Result:

No results yet. Enter the required values above.

How to use stoichiometry calculator

1) Enter a balanced chemical equation (include coefficients).
2) Choose the known and target species from the dropdowns.
3) Select the known amount type (moles, mass, or particles) and enter its value. If you choose mass, provide the known species’ molar mass.
4) Select the target quantity type. If mass, provide the target’s molar mass.
5) Click Calculate Stoichiometry.

Key Points

Mole ratios come from the balanced equation’s coefficients.
Convert the known amount to moles, apply the mole ratio, then convert to the desired unit.
Use particles = moles × 6.022×10²³ (Avogadro’s number).

Formula & Equation Used

From a balanced equation, the mole ratio is given by coefficients:

n_{target} = n_{known} \times \frac{ν_{target}}{ν_{known}}

n: moles, ν: stoichiometric coefficient
mass = moles × molar mass
particles = moles × N_A (6.022×10²³)

Example Problem & Step-by-Step Solution

Problem 1:

How many grams of H₂O form from 5.00 g H₂ (excess O₂)?

Solution:

Balanced: 2 H₂ + O₂ = 2 H₂O
Moles H₂ = 5.00 g ÷ 2.016 g/mol = 2.480 mol
Mole ratio H₂ → H₂O = 2:2 ⇒ n(H₂O) = 2.480 mol
Mass H₂O = 2.480 mol × 18.015 g/mol = 44.7 g

Problem 2:

How many liters of CO₂ (at STP) are produced from 10.0 g of CaCO₃ when it decomposes completely?

Solution:

Balanced: CaCO₃ → CaO + CO₂
Moles CaCO₃ = 10.0 g ÷ 100.09 g/mol = 0.0999 mol
Mole ratio CaCO₃ → CO₂ = 1:1 ⇒ n(CO₂) = 0.0999 mol
At STP, 1 mol gas = 22.4 L ⇒ Volume CO₂ = 0.0999 mol × 22.4 L/mol = 2.24 L

Frequently Asked Questions

Q: How do you calculate moles from grams?

Divide the mass of the substance (in grams) by its molar mass (g/mol).

Q: What is molar mass?

Molar mass is the mass of one mole of a substance, usually measured in g/mol. It equals the atomic or molecular weight from the periodic table.

Q: Why are moles important in chemistry?

Moles connect measurable amounts (grams) to the actual number of atoms, molecules, or ions. They are the foundation for stoichiometry and chemical equations.

Calculating Molar Mass