Molar Mass Table of Common Compounds

One mole of water (H₂O) has a mass of 18.015 grams. That is its molar mass. The molar mass of sodium chloride (NaCl) is 58.44 g/mol. The molar mass of carbon dioxide (CO₂) is 44.01 g/mol. These numbers come from the IUPAC CIAAW Standard Atomic Weights (2021 edition, ciaaw.org). This table gives you the value to plug into the conversion n = m / M (moles = mass divided by molar mass). The mole is a counting unit like a dozen, but for particles: one mole always contains exactly 6.02214076 × 10²³ particles (Avogadro's constant, fixed in the 2019 SI redefinition, BIPM SI Brochure 9th ed.).

The molar mass of water is 18.015 g/mol. The calculation: two hydrogen atoms (2 × 1.008 g/mol = 2.016) plus one oxygen atom (15.999 g/mol) equals 18.015 g/mol. This is the value used in lab work and textbook problems. The most common mistake is rounding to 18 g/mol. That 0.015 g/mol gap accumulates when you scale up. For a 5-mole sample, the error becomes 0.075 grams. In precise stoichiometry, use the full value. For high-school homework, many teachers accept 18.0 g/mol. Check the problem's required significant figures before you round.

The molar mass of NaCl is 58.44 g/mol. Sodium (22.990 g/mol) plus chlorine (35.45 g/mol) gives 58.44 g/mol. This is the value for table salt. If you are preparing a 1 M solution, weigh out 58.44 grams of NaCl and dissolve it in enough water to make 1 liter of solution. The error newcomers make is using the atomic mass of chlorine as 35.5 from an old periodic table. The IUPAC CIAAW 2021 value is 35.45 g/mol. The difference is small for one mole but matters in multi-mole preparations.

The molar mass of CO₂ is 44.01 g/mol. Carbon (12.011 g/mol) plus two oxygen atoms (2 × 15.999 g/mol = 31.998 g/mol) equals 44.01 g/mol (rounded to two decimal places). This is the number you use in combustion analysis and gas law calculations. The failure case: using 44 g/mol instead of 44.01 g/mol.0052 moles, negligible for homework, but avoidable. Use the precise value from this table.

Below are the molar masses of compounds you will encounter most often in high school and first-year college chemistry. Every value is computed from IUPAC CIAAW 2021 atomic weights, rounded to the same convention used in standard textbooks: two decimal places for compounds with multiple elements, three decimal places for diatomic gases. The conversion n = m / M is the same for every substance. A higher molar mass means fewer moles for the same mass.

Molar Masses of Common Compounds

Water (H₂O): 18.015 g/mol. Sodium chloride (NaCl): 58.44 g/mol. Carbon dioxide (CO₂): 44.01 g/mol. Glucose (C₆H₁₂O₆): 180.156 g/mol. Sodium hydroxide (NaOH): 39.997 g/mol. Calcium carbonate (CaCO₃): 100.09 g/mol.Ethanol (C₂H₅OH): 46.07 g/mol. Ammonia (NH₃): 17.031 g/mol. Oxygen gas (O₂): 31.998 g/mol. Hydrogen gas (H₂): 2.016 g/mol.

Molar Masses of Common Elements

Carbon (C): 12.011 g/mol. Iron (Fe): 55.845 g/mol. Sodium (Na): 22.990 g/mol. Chlorine (Cl): 35.45 g/mol. Oxygen (O): 15.999 g/mol. Hydrogen (H): 1.008 g/mol. These elemental values are the atomic weights from IUPAC CIAAW 2021.

Each compound molar mass is the sum of the atomic masses of all atoms in its chemical formula. You take the atomic weight of each element from the IUPAC CIAAW Standard Atomic Weights table (2021 edition, ciaaw.org). Multiply by the number of atoms of that element in the formula. Add the products. The result has units of grams per mole (g/mol). The same number, in atomic mass units (amu), is the formula mass. They are numerically equal. The Avogadro constant (6.02214076 × 10²³ mol⁻¹) is the bridge that makes this work: one mole of a substance contains that many formula units.

Most textbooks round molar masses to two decimal places for compounds with more than one element. They round to three decimal places for diatomic elements (O₂, H₂, N₂) and to one decimal place for simple ionic compounds in some introductory texts. The IUPAC CIAAW atomic weights themselves have varying uncertainties. For example, the atomic weight of carbon is 12.011 g/mol with a standard uncertainty of 0.001 g/mol. The atomic weight of chlorine is 35.45 g/mol with an uncertainty of 0.01 g/mol. The molar mass table here uses the same rounding as a standard lab reference: two decimals for most compounds, three for diatomic gases and glucose. Always check the significant figures in your problem. The highest precision you can report is limited by the least precise atomic weight in the formula. For sodium chloride, the chlorine value (35.45) has four significant figures, so the molar mass (58.44) has four significant figures.

The most frequent error is using the atomic mass of an element instead of the molecular mass of a compound. For oxygen gas (O₂), use 31.998 g/mol, not 15.999 g/mol. For hydrogen gas (H₂), use 2.016 g/mol, not 1.008 g/mol. The second most common failure is forgetting to multiply the atomic weight by the number of atoms in the formula. For glucose (C₆H₁₂O₆), you multiply carbon by 6, hydrogen by 12, and oxygen by 6 before adding. The third failure is using mass in kilograms instead of grams. The formula n = m / M requires mass in grams. A 2-kilogram sample is 2000 grams. The fourth failure: rounding intermediate values too aggressively. Round only the final answer to the correct number of significant figures. If you round the atomic weight of oxygen to 16 g/mol before adding it to the formula, your molar mass for water becomes 18 g/mol instead of 18.015 g/mol, introducing an error of 0.08%.

High-school chemistry students who need to complete homework problems involving mass-to-mole conversions and stoichiometry will use this table for a fast, accurate value. First-year college chemistry students checking their work on lab reports and problem sets will find the precision to the correct number of significant figures. Lab technicians preparing solutions of a specific molarity from a solid reagent will use the reliable molar mass of common compounds. Tutors and teachers who need a reference tool to demonstrate the conversion process and verify example problems will also benefit.

Anyone looking for a theoretical derivation of the mole concept from first principles, or a history of Avogadro's number, should go to OpenStax Chemistry or a general chemistry textbook. This table is a calculation tool, not a textbook. The conversion from grams to moles is a simple division: moles = mass (g) / molar mass (g/mol). The most common mistake newcomers make is treating the molar mass as a fixed number for every substance, when it is substance-specific and must be calculated from the periodic table.