Molar Mass Calculator
The molar mass of a substance from its chemical formula: the atoms of each element, their contributions and mass fractions, by IUPAC standard atomic weights
Molar Mass Calculator
Molar Mass
Molar mass is the mass of one mole of a substance: the sum of the atomic weights of all the atoms in its formula, in g/mol.
Example: H2SO4
M(H2SO4) ≈ 98.07 g/mol
| Element | Atoms, n | Atomic weight, A | n × A, g/mol Mass fraction, w | |
|---|---|---|---|---|
| Hhydrogen | 2 | 1.0080 | 2.0160 w ≈ 2.06% | ≈ 2.06% |
| Ssulfur | 1 | 32.06 | 32.06 w ≈ 32.69% | ≈ 32.69% |
| Ooxygen | 4 | 15.999 | 63.996 w ≈ 65.25% | ≈ 65.25% |
| Σ = 98.072 ≈ 98.07 g/mol w = 100% | 100% | |||
Atomic weights: CIAAW, Abridged Standard Atomic Weights (2024)
O 65.25%
S 32.69%H 2.06%
| Z | Element | M, g/mol |
|---|---|---|
| 1 | H — hydrogen | 1.0080 |
| 2 | He — helium | 4.0026 |
| 3 | Li — lithium | 6.94 |
| 4 | Be — beryllium | 9.0122 |
| 5 | B — boron | 10.81 |
| 6 | C — carbon | 12.011 |
| 7 | N — nitrogen | 14.007 |
| 8 | O — oxygen | 15.999 |
| 9 | F — fluorine | 18.998 |
| 10 | Ne — neon | 20.180 |
| 11 | Na — sodium | 22.990 |
| 12 | Mg — magnesium | 24.305 |
| 13 | Al — aluminium | 26.982 |
| 14 | Si — silicon | 28.085 |
| 15 | P — phosphorus | 30.974 |
| 16 | S — sulfur | 32.06 |
| 17 | Cl — chlorine | 35.45 |
| 18 | Ar — argon | 39.95 |
| 19 | K — potassium | 39.098 |
| 20 | Ca — calcium | 40.078 |
| 21 | Sc — scandium | 44.956 |
| 22 | Ti — titanium | 47.867 |
| 23 | V — vanadium | 50.942 |
| 24 | Cr — chromium | 51.996 |
| 25 | Mn — manganese | 54.938 |
| 26 | Fe — iron | 55.845 |
| 27 | Co — cobalt | 58.933 |
| 28 | Ni — nickel | 58.693 |
| 29 | Cu — copper | 63.546 |
| 30 | Zn — zinc | 65.38 |
| 31 | Ga — gallium | 69.723 |
| 32 | Ge — germanium | 72.630 |
| 33 | As — arsenic | 74.922 |
| 34 | Se — selenium | 78.971 |
| 35 | Br — bromine | 79.904 |
| 36 | Kr — krypton | 83.798 |
| 37 | Rb — rubidium | 85.468 |
| 38 | Sr — strontium | 87.62 |
| 39 | Y — yttrium | 88.906 |
| 40 | Zr — zirconium | 91.222 |
| 41 | Nb — niobium | 92.906 |
| 42 | Mo — molybdenum | 95.95 |
| 44 | Ru — ruthenium | 101.07 |
| 45 | Rh — rhodium | 102.91 |
| 46 | Pd — palladium | 106.42 |
| 47 | Ag — silver | 107.87 |
| 48 | Cd — cadmium | 112.41 |
| 49 | In — indium | 114.82 |
| 50 | Sn — tin | 118.71 |
| 51 | Sb — antimony | 121.76 |
| 52 | Te — tellurium | 127.60 |
| 53 | I — iodine | 126.90 |
| 54 | Xe — xenon | 131.29 |
| 55 | Cs — caesium | 132.91 |
| 56 | Ba — barium | 137.33 |
| 57 | La — lanthanum | 138.91 |
| 58 | Ce — cerium | 140.12 |
| 59 | Pr — praseodymium | 140.91 |
| 60 | Nd — neodymium | 144.24 |
| 62 | Sm — samarium | 150.36 |
| 63 | Eu — europium | 151.96 |
| 64 | Gd — gadolinium | 157.25 |
| 65 | Tb — terbium | 158.93 |
| 66 | Dy — dysprosium | 162.50 |
| 67 | Ho — holmium | 164.93 |
| 68 | Er — erbium | 167.26 |
| 69 | Tm — thulium | 168.93 |
| 70 | Yb — ytterbium | 173.05 |
| 71 | Lu — lutetium | 174.97 |
| 72 | Hf — hafnium | 178.49 |
| 73 | Ta — tantalum | 180.95 |
| 74 | W — tungsten | 183.84 |
| 75 | Re — rhenium | 186.21 |
| 76 | Os — osmium | 190.23 |
| 77 | Ir — iridium | 192.22 |
| 78 | Pt — platinum | 195.08 |
| 79 | Au — gold | 196.97 |
| 80 | Hg — mercury | 200.59 |
| 81 | Tl — thallium | 204.38 |
| 82 | Pb — lead | 207.2 |
| 83 | Bi — bismuth | 208.98 |
| 90 | Th — thorium | 232.04 |
| 91 | Pa — protactinium | 231.04 |
| 92 | U — uranium | 238.03 |
| Substance | M, g/mol |
|---|---|
| H₂O (water) | 18.015 |
| NaCl (sodium chloride) | 58.44 |
| CO₂ (carbon dioxide) | 44.009 |
| H₂SO₄ (sulfuric acid) | 98.07 |
| NaOH (sodium hydroxide) | 39.997 |
| CH₄ (methane) | 16.043 |
| C₆H₁₂O₆ (glucose) | 180.156 |
| C₁₂H₂₂O₁₁ (sucrose) | 342.297 |
Common mistakes
- CO and Co are different substances: M(CO) = 28.010 g/mol (carbon monoxide), M(Co) = 58.933 g/mol (cobalt). Write each symbol with a capital letter: a lowercase letter continues the symbol before it.
- An oxygen atom and oxygen gas are not the same: M(O) = 15.999 g/mol, while the gas is made of molecules, M(O₂) = 31.998 g/mol. In a gas problem, «the molar mass of oxygen» usually means O₂.
- Chemistry uses g/mol, SI and physics use kg/mol: M(H₂SO₄) ≈ 98.07 g/mol = 0.09807 kg/mol. Mixing them makes the answer 1,000 times off.
- The water of a crystal hydrate counts: M(CuSO₄·5H₂O) ≈ 249.68 g/mol, while without the water M(CuSO₄) ≈ 159.60 g/mol.
See Also
- Liters to Kilograms - How many kilograms are in a liter of water, honey, gasoline, sand and other substances — by density
- Grams to Kg - Convert Grams to Kilograms
- Percentage Calculator: Fraction to Percent - What percentage one number is of another? Convert fraction into a percentage
- Scientific Calculator with Memory & History - Free Engineering Calculator Online with Memory Function, Operation History, Logarithms & Trigonometry. Similar to ti-83, ti-84, ti-89
FAQ
How to find the molar mass from a chemical formula?
Multiply the atomic weight of each element by the number of its atoms and add everything up. For H₂SO₄: 2 × 1.0080 + 32.06 + 4 × 15.999 = 98.072 ≈ 98.07 g/mol. Brackets multiply everything inside them, and the water of a hydrate counts too.
What is the difference between molar mass and molecular mass?
The number is the same, the meaning differs: the molecular mass of H₂SO₄ is 98.07 u (daltons) — the mass of one molecule; the molar mass is 98.07 g/mol — the mass of one mole, 6.022 × 10²³ molecules.
Why do school problems use round numbers?
Textbooks round atomic weights to whole numbers (chlorine to 35.5) so the sums are easy to do by hand: H₂SO₄ gives 2·1 + 32 + 4·16 = 98 g/mol. The IUPAC table gives 2 × 1.0080 + 32.06 + 4 × 15.999 = 98.072 ≈ 98.07 g/mol; for lab work, use the table values.
How to convert grams to moles?
Divide the mass by the molar mass: n = m / M. For example, 49.035 g of H₂SO₄ is 49.035 ÷ 98.07 = 0.5 mol. Back: m = n × M.