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Molar Mass Calculator
Calculate molar mass from chemical formulas with parentheses support and all 118 elements. Includes grams-to-moles conversion, composition breakdown, percent bars, and common compound presets.
H2O
Molar Mass⧉
18.0150 g/mol
18.0150 Da
Total Atoms per Molecule⧉
3
2 elements
Grams ↔ Moles Converter
Enter either mass or moles to convert. Based on M = 18.0150 g/mol.
g
mol
Elemental Composition
| Element | Atoms | Atomic Mass | Contribution | Mass % |
|---|---|---|---|---|
| H (Hydrogen) | 2 | 1.008 g/mol | 2.016 g/mol | 11.19% |
| O (Oxygen) | 1 | 15.999 g/mol | 15.999 g/mol | 88.81% |
Common Compound Reference
| Compound | Formula | Molar Mass (g/mol) |
|---|---|---|
| Water ← current | H2O | 18.0150 |
| Sodium chloride | NaCl | 58.4400 |
| Carbon dioxide | CO2 | 44.0090 |
| Glucose | C6H12O6 | 180.1560 |
| Sulfuric acid | H2SO4 | 98.0720 |
| Sodium hydroxide | NaOH | 39.9970 |
| Ethanol | C2H5OH | 46.0690 |
| Ammonia | NH3 | 17.0310 |
Atomic masses from IUPAC 2021 standard atomic weights. Supports all 118 elements and parenthesized groups like Ca(OH)₂.
Planning notes, formulas, and examples
About the Molar Mass Calculator
Molar mass — the mass of one mole of a substance, expressed in grams per mole (g/mol) — is the most fundamental quantity in stoichiometry. It is the bridge between the atomic scale and the laboratory scale: to convert between grams and moles, you need the molar mass; to balance equations and predict reaction yields, you need moles; therefore molar mass is the starting point for nearly every quantitative chemistry calculation.
This calculator parses a standard chemical formula and quickly returns the molar mass along with a full elemental composition breakdown. You can see how many atoms of each element are present, their individual atomic masses, their mass contributions, and their percentage by mass. It supports all common elements and handles compounds from simple (NaCl, H2O) to moderately complex (C6H12O6, Ca3PO42 written as Ca3P2O8).
Whether you are a student doing homework, a lab technician preparing solutions, or a researcher computing reagent quantities, This calculator eliminates the repetitive lookup-and-multiply process that makes molar mass calculations tedious by hand.
When This Page Helps
Calculating molar mass by hand requires looking up each element in the periodic table, multiplying by the number of atoms, and summing — a process that is error-prone for larger molecules. This calculator does it quickly and also provides a percent composition breakdown, which is useful for analytical chemistry, empirical formula determination, and gravimetric analysis.
How to Use the Inputs
- Type a chemical formula into the input field using standard notation (e.g., H2O, NaCl, C6H12O6).
- Use parentheses for polyatomic groups: Ca(OH)2, Mg3(PO4)2, Al2(SO4)3.
- Or click a common compound preset button to auto-fill the formula.
- The molar mass in g/mol and total atoms per molecule are displayed immediately.
- Use the Grams ↔ Moles converter: enter a mass to get moles, or enter moles to get grams and molecule count.
- Review the composition table showing atom counts, mass contributions, and visual percentage bars.
- Check the common compounds reference table — your current compound is highlighted if it matches.
Formula used
Molar Mass (M) = Σ (nᵢ × Aᵢ)
Where:
nᵢ = number of atoms of element i in the formula
Aᵢ = atomic mass of element i (from the periodic table, in g/mol)
Mass Percent of element i:
%mᵢ = (nᵢ × Aᵢ) / M × 100%
Example: H₂O
M = 2(1.008) + 1(15.999) = 18.015 g/mol
%H = 2(1.008)/18.015 × 100% = 11.19%
%O = 15.999/18.015 × 100% = 88.81%Example Calculation
Result: 180.156 g/mol
Glucose (C₆H₁₂O₆) contains 6 carbon atoms (6 × 12.011 = 72.066), 12 hydrogen atoms (12 × 1.008 = 12.096), and 6 oxygen atoms (6 × 15.999 = 95.994). Summing: 72.066 + 12.096 + 95.994 = 180.156 g/mol. Carbon contributes 40.00%, hydrogen 6.71%, and oxygen 53.29% by mass.
Tips & Best Practices
- Molar mass is numerically equal to the molecular weight (MW) or formula weight (FW) — different terms, same number.
- One mole equals 6.022 × 10²³ particles (Avogadro's number). The molar mass tells you how many grams that many particles weigh.
- For ionic compounds like NaCl, the term "formula weight" is technically correct since they do not form discrete molecules.
- Mass percent composition is useful for determining empirical formulas from experimental data.
- Always double-check element symbols: Co (cobalt) ≠ CO (carbon + oxygen).
- For hydrates, add the water separately: CuSO4·5H2O → compute CuSO4 (159.61) + 5×H2O (90.08) = 249.69 g/mol.
Why Molar Mass Is Central to Chemistry
Every quantitative calculation in chemistry — from balancing equations to determining concentrations to computing reaction yields — passes through moles at some point. Molar mass is the conversion factor that connects the macroscopic world (grams, liters) to the atomic world (atoms, molecules). Without it, you cannot move between what you weigh on a balance and what actually reacts at the molecular level.
Molar Mass in Lab Practice
When preparing a solution of known molarity, you calculate the required mass of solute using molar mass: mass = molarity × volume × molar mass. In titrations, molar mass converts between moles of reactant and grams for weighing. In gravimetric analysis, molar mass and percent composition help determine the amount of an analyte from the mass of a precipitate.
Common Molar Masses Worth Memorizing
- Water (H₂O): 18.015 g/mol - Carbon dioxide (CO₂): 44.009 g/mol - Sodium chloride (NaCl): 58.443 g/mol - Glucose (C₆H₁₂O₆): 180.156 g/mol - Sulfuric acid (H₂SO₄): 98.079 g/mol - Ethanol (C₂H₅OH): 46.069 g/mol
Having these reference points helps you quickly estimate whether a calculated result is in the right ballpark.
Sources & Methodology
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Frequently Asked Questions
Molar mass is the mass of one mole (6.022 × 10²³ particles) of a substance, expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in the chemical formula. For example, water (H₂O) has a molar mass of 18.015 g/mol.
They are numerically the same. Molar mass is expressed in g/mol and refers to one mole of substance, while molecular weight (or relative molecular mass) is a dimensionless ratio of the mass of a molecule to 1/12 of a carbon-12 atom. In practice, chemists use them interchangeably.
Divide the mass in grams by the molar mass: moles = grams ÷ M. For example, 36 g of water ÷ 18.015 g/mol = 2.0 mol. To convert moles to grams, multiply: grams = moles × M.
Atomic masses on the periodic table are weighted averages of all naturally occurring isotopes of that element. For example, chlorine is 75.76% Cl-35 and 24.24% Cl-37, giving an average atomic mass of 35.45, not a whole number.
Yes! Enter formulas like Ca(OH)2, Mg3(PO4)2, or Al2(SO4)3 directly. The parser handles nested parentheses and subscripts correctly, computing accurate molar masses for complex compounds.
Percent composition (or mass percent) is the fraction of a compound's total mass contributed by each element, expressed as a percentage. It is useful for analytical chemistry tasks like determining empirical formulas from combustion analysis data.