Molar Mass Calculator
Find the molar mass of common elements and chemical compounds in g/mol. Instantly convert between moles, grams, and molecules.
Molar Mass
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Moles —
Grams —
Molecules (×10²³) —
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Moles (mol)
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Molar Mass (g/mol) —
Molecules (×10²³) —
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Molar Mass (g/mol)
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Moles (mol) —
Grams (g) —
Molecules (×10²³) —
Molarity (mol/L) —
Ideal Gas Volume (L) —
Mass per mol —
How to Use This Calculator
- Select a compound or element from the list.
- Enter the amount in grams or moles.
- Results show moles, grams, and number of molecules.
Formula
Grams = Moles × Molar mass
Moles = Grams ÷ Molar mass
Molecules = Moles × 6.022 × 10²³
Example
Example: 36.03 g of water (M = 18.015 g/mol) → 2.000 mol → 1.204 × 10²⁴ molecules.
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). For elements, molar mass equals the atomic weight listed on the periodic table. For compounds, add the molar masses of all atoms in the molecular formula. For example, carbon dioxide (CO₂) has molar mass = C (12.011) + 2 × O (15.999) = 44.009 g/mol. Molar mass links the macroscopic (grams) and microscopic (atoms/molecules) scales of chemistry. It is the conversion factor between moles and grams in stoichiometry calculations.
- Water (H₂O) has a molar mass of 18.015 g/mol, calculated as: 2 × H (1.008) + O (15.999) = 2.016 + 15.999 = 18.015 g/mol. One mole of water = 18.015 grams and contains 6.022 × 10²³ water molecules. At room temperature, 18 mL of pure water (about 1 tablespoon) is very close to one mole. This is a fundamental reference value in chemistry. Two moles of water = 36.03 g, and half a mole = 9.008 g.
- Multiply moles by the molar mass (g/mol) to get grams: Grams = Moles × Molar mass. For example, 2 mol of sodium chloride (NaCl, molar mass = 22.990 + 35.453 = 58.44 g/mol): 2 × 58.44 = 116.88 g. For 0.5 mol of glucose (C₆H₁₂O₆, molar mass = 180.16 g/mol): 0.5 × 180.16 = 90.08 g. This conversion is used constantly in laboratory chemistry for preparing solutions of a known molar concentration. The molar mass value for each compound is shown in this calculator.
- Divide the mass in grams by the molar mass (g/mol) to get moles: Moles = Grams ÷ Molar mass. For example, 100 g of NaCl (molar mass 58.44 g/mol): 100 ÷ 58.44 = 1.711 mol. For 54 g of water (molar mass 18.015 g/mol): 54 ÷ 18.015 = 3.0 mol. This is the first step in most stoichiometry problems — convert grams to moles, use mole ratios from the balanced equation, then convert back to grams. Enter grams in the first field of this calculator and the moles are shown instantly.
- Avogadro's number (N_A) is 6.02214076 × 10²³ entities per mole — this is the number of atoms, molecules, ions, or electrons in exactly one mole of a substance. It was defined exactly in the 2019 revision of the SI system. To find the number of molecules in a sample: Molecules = Moles × N_A. For example, 2 mol of CO₂ contains 2 × 6.022 × 10²³ = 1.204 × 10²⁴ molecules. The number is named after Amedeo Avogadro, who first proposed that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. This calculator shows molecule counts in scientific notation.