Molar mass calculator
Type any chemical formula, such as H₂SO₄, Ca(OH)₂ or CuSO₄·5H₂O, and get its molar mass in g/mol together with the percentage of each element by mass. Free, instant and works on your phone.
⚖️ Open the molar mass calculatorHow to calculate molar mass
- Write the chemical formula and count the atoms of each element. A number after brackets multiplies everything inside them.
- Look up each element’s atomic mass on the periodic table.
- Multiply each atomic mass by the number of atoms of that element.
- Add the results. The total is the molar mass in g/mol.
Worked example: copper(II) sulfate pentahydrate
1 × 63.546 + 1 × 32.065 + 9 × 15.999 + 10 × 1.008 = 249.68 g/mol
| Element | Atoms | Atomic mass (u) | Subtotal (g/mol) | % by mass |
|---|---|---|---|---|
| Copper (Cu) | 1 | 63.546 | 63.546 | 25.45% |
| Sulfur (S) | 1 | 32.065 | 32.065 | 12.84% |
| Oxygen (O) | 9 | 15.999 | 143.991 | 57.67% |
| Hydrogen (H) | 10 | 1.008 | 10.080 | 4.04% |
| Molar mass of CuSO4·5H2O | 249.68 g/mol | |||
Molar masses of common compounds
| Formula | Name | Molar mass (g/mol) |
|---|---|---|
| H2O | Water | 18.02 |
| CO2 | Carbon dioxide | 44.01 |
| NaCl | Sodium chloride | 58.44 |
| H2SO4 | Sulfuric acid | 98.08 |
| HCl | Hydrogen chloride (hydrochloric acid) | 36.46 |
| NaOH | Sodium hydroxide | 40.00 |
| C6H12O6 | Glucose | 180.16 |
| CaCO3 | Calcium carbonate | 100.09 |
| NH3 | Ammonia | 17.03 |
| CH4 | Methane | 16.04 |
| O2 | Oxygen | 32.00 |
| N2 | Nitrogen | 28.01 |
| H2 | Hydrogen | 2.02 |
| HNO3 | Nitric acid | 63.01 |
| KMnO4 | Potassium permanganate | 158.03 |
| CuSO4 | Copper(II) sulfate (anhydrous) | 159.61 |
| CuSO4·5H2O | Copper(II) sulfate pentahydrate | 249.68 |
| NaHCO3 | Sodium bicarbonate | 84.01 |
| Na2CO3 | Sodium carbonate | 105.99 |
| C12H22O11 | Sucrose | 342.30 |
| C2H5OH | Ethanol | 46.07 |
| CH3COOH | Acetic acid | 60.05 |
| Ca(OH)2 | Calcium hydroxide | 74.09 |
| KOH | Potassium hydroxide | 56.11 |
| MgO | Magnesium oxide | 40.30 |
| Fe2O3 | Iron(III) oxide | 159.69 |
| Al2O3 | Aluminium oxide | 101.96 |
| H2O2 | Hydrogen peroxide | 34.01 |
| KCl | Potassium chloride | 74.55 |
| AgNO3 | Silver nitrate | 169.87 |
| Pb(NO3)2 | Lead(II) nitrate | 331.21 |
| KI | Potassium iodide | 166.00 |
| (NH4)2SO4 | Ammonium sulfate | 132.14 |
| H3PO4 | Phosphoric acid | 97.99 |
| CaCl2 | Calcium chloride | 110.98 |
| MgSO4 | Magnesium sulfate | 120.37 |
| KNO3 | Potassium nitrate | 101.10 |
| C3H8 | Propane | 44.10 |
| SO2 | Sulfur dioxide | 64.06 |
| NH4Cl | Ammonium chloride | 53.49 |
| BaCl2 | Barium chloride | 208.24 |
| Na2SO4 | Sodium sulfate | 142.04 |
Frequently asked questions
What is molar mass?
Molar mass is the mass of one mole of a substance, measured in grams per mole (g/mol). One mole contains 6.022 × 10²³ particles (Avogadro’s number). Numerically it equals the relative formula mass.
How do you calculate molar mass?
Write the formula, count the atoms of each element, multiply each count by that element’s atomic mass from the periodic table, and add the results. Brackets multiply everything inside them, and a hydrate such as ·5H₂O adds five water molecules.
What is the difference between molar mass and molecular weight?
They have the same number. Molecular weight (relative molecular mass) has no units, while molar mass is in g/mol. For water both are about 18.02.