What Is a Stoichiometry Calculator?
A stoichiometry calculator connects measured quantities with the mole ratios in a balanced chemical equation. This page also works as a molar mass calculator: enter a chemical formula to obtain its mass per mole, atom counts, element contributions, and percentage composition. Together, those operations cover the central path used in introductory reaction calculations.
The calculator does not guess products or balance an equation. You supply the known and target formulas plus their coefficients from an equation that is already balanced. Keeping those inputs explicit makes the dimensional analysis visible and prevents a chemically invalid equation from being presented as a valid numerical result.
How to Calculate Molar Mass from a Chemical Formula
Molar mass is found by multiplying each element's atom count by its atomic weight and adding every contribution. In H₂O, two hydrogen atoms contribute about 2.016 and one oxygen atom contributes 15.999, giving 18.015 g/mol with the atomic weights used here. Parentheses multiply a complete group, so Ca(OH)₂ contains two oxygen atoms and two hydrogen atoms.
The formula parser recognizes standard element capitalization, nested parentheses or square brackets, and hydrate notation such as CuSO₄·5H₂O. A hydrate coefficient applies to the complete segment after the middle dot. Ionic charges, isotope notation, structural abbreviations, and reaction coefficients inside formula fields are intentionally rejected because they require different parsing rules.
How Mole Ratios Work in a Balanced Equation
Coefficients in a balanced equation describe relative amounts in moles. In 2H₂ + O₂ → 2H₂O, two moles of hydrogen correspond to one mole of oxygen and two moles of water. To move from a known substance to a target substance, multiply known moles by target coefficient divided by known coefficient.
Coefficients are ratios, so scaling all coefficients by the same factor does not change the answer. Subscripts are different: they are part of a substance's identity and cannot be changed while balancing an equation. H₂O and H₂O₂ are different compounds, not two ways of writing the same material.
Stoichiometry Conversion: Grams, Moles, and Particles
Moles form the bridge between macroscopic mass and microscopic entities. Convert grams to moles by dividing by molar mass. Convert particles to moles by dividing by the exact Avogadro constant, 6.02214076 × 10²³ mol⁻¹. After applying the coefficient ratio, reverse the appropriate operation to obtain target grams or particles.
| Convert from | Convert to moles | Convert moles to target |
|---|---|---|
| Grams | moles = grams ÷ molar mass | grams = moles × molar mass |
| Particles | moles = particles ÷ 6.02214076×10²³ | particles = moles × 6.02214076×10²³ |
| Moles | No conversion | No conversion |
“Particles” means specified representative entities. Use molecules for molecular compounds, formula units for ionic compounds, atoms for monatomic elements, or another entity explicitly named by the chemical statement.
Worked Stoichiometry and Molar Mass Examples
Suppose 4.00 mol H₂ reacts according to 2H₂ + O₂ → 2H₂O. The H₂-to-H₂O coefficient ratio is 2/2, so the calculation gives 4.00 mol H₂O. Multiplying by the water molar mass, 18.015 g/mol, gives 72.06 g H₂O before any rounding required by measured-value precision.
For a mass-to-mass example, 32 g O₂ is approximately one mole when O₂ has a molar mass of 31.998 g/mol. The equation C + O₂ → CO₂ uses a 1:1 ratio, producing approximately one mole of CO₂, whose molar mass is 44.009 g/mol. Actual laboratory yield may be lower because this ideal calculation does not model purity, limiting reagents, or percent yield.
Chemical Formula and Atomic Weight Reference
The calculator includes all 118 named elements and uses conventional values based on the CIAAW 2024 standard atomic-weight table. Elements without a standard atomic weight use a bracket-style representative isotope mass number. Naturally variable isotopic composition means a high-precision laboratory molar mass can differ slightly from a conventional classroom value.
Formula capitalization is exact. An uppercase letter begins an element symbol and an optional lowercase letter completes it: Na is sodium, while NA is not an element symbol. This distinction is essential because CO represents carbon and oxygen, whereas Co is the single element cobalt.
Stoichiometry Calculator FAQ
How do I calculate molar mass from a chemical formula?
Count each element's atoms, multiply each count by its atomic weight, then add the contributions. Parentheses multiply every atom inside the group, while hydrate coefficients multiply the following formula segment.
How do I use coefficients in a stoichiometry calculation?
Take coefficients from a balanced chemical equation and form target coefficient divided by known coefficient. Multiply the known amount in moles by that ratio to find target moles.
Can this calculator balance a chemical equation?
No. This calculator uses coefficients you supply from an equation that is already balanced, so verify atom conservation before calculating.
What is the difference between molar mass and molecular weight?
Molar mass is the mass of one mole and is commonly reported in grams per mole. Relative molecular mass compares a molecule with the atomic mass constant and is dimensionless.
How many particles are in one mole?
One mole contains exactly 6.02214076 × 10²³ specified entities. Those entities may be molecules, formula units, atoms, ions, or another explicitly identified particle.
Why does capitalization matter in a chemical formula?
Element symbols are case-sensitive: CO means carbon monoxide, whereas Co is cobalt. The calculator preserves capitalization and rejects symbols that are not valid elements.