What is the molar mass?
Type a chemical formula such as H2O or CuSO4·5H2O. The molar mass calculator adds up the atomic weights, shows each element's share by mass, and converts grams to moles.
- Molar mass
- 180.156
The molar mass of C₆H₁₂O₆ is 180.156 g/mol.
- Formula
- C₆H₁₂O₆
- Composition by mass
- C: 6 × 12.011 = 72.066 g/mol (40.002%); H: 12 × 1.008 = 12.096 g/mol (6.714%); O: 6 × 15.999 = 95.994 g/mol (53.284%)
- Atoms in the formula
- 24
Molar mass: 180.156. The molar mass of C₆H₁₂O₆ is 180.156 g/mol.
How is the molar mass added up?
How to calculate
Computes the molar mass (molecular weight) of a chemical formula in g/mol from the IUPAC standard atomic weights, with each element’s share by mass, and converts grams to moles and moles to grams.
Example with the default inputs (Chemical formula C6H12O6): The molar mass of C₆H₁₂O₆ is 180.156 g/mol.
Method: molar mass = Σ (atoms of each element × its standard atomic weight), in g/mol; moles = grams ÷ molar mass.
- Atomic weights are the CIAAW abridged standard atomic weights (2024), the values printed on most periodic tables: for example H 1.0080, C 12.011, O 15.999, Na 22.990, Cl 35.45.
- Elements with no standard atomic weight (technetium, promethium, and polonium onward except thorium, protactinium and uranium) give no answer.
- A charge does not change the molar mass here: the mass of the electrons gained or lost is left out. A phase label such as (aq) is ignored.
- A whole number typed before the formula multiplies it (2H2O is two water molecules, 36.030 g/mol).
Worked examples
Each example is checked against the calculator on every build.
- Chemical formula H2O gives Molar mass 18.015, Composition by mass H: 2 × 1.008 = 2.016 g/mol (11.191%); O: 1 × 15.999 = 15.999 g/mol (88.809%), Atoms in the formula 3.Source: CIAAW, Abridged Standard Atomic Weights (H 1.0080, O 15.999), https://ciaaw.org/abridged-atomic-weights.htm
- Chemical formula C6H12O6, Mass of sample 90 g gives Molar mass 180.156, Formula C₆H₁₂O₆, Moles in the sample 0.499567, Atoms in the formula 24.Source: CIAAW, Abridged Standard Atomic Weights (C 12.011, H 1.0080, O 15.999), https://ciaaw.org/abridged-atomic-weights.htm
- Chemical formula NaCl, Amount (mol) 2 gives Molar mass 58.44, Mass of the amount 116.88.Source: CIAAW, Abridged Standard Atomic Weights (Na 22.990, Cl 35.45), https://ciaaw.org/abridged-atomic-weights.htm
- Chemical formula CuSO4·5H2O gives Molar mass 249.677, Formula CuSO₄·5H₂O, Atoms in the formula 21.Source: 63.546 + 32.06 + 9 × 15.999 + 10 × 1.0080 = 249.677 (weights from CIAAW, https://ciaaw.org/abridged-atomic-weights.htm)
- Chemical formula Ca(OH)2 gives Molar mass 74.092, Formula Ca(OH)₂, Atoms in the formula 5.Source: 40.078 + 2 × 15.999 + 2 × 1.0080 = 74.092 (CIAAW, https://ciaaw.org/abridged-atomic-weights.htm)
- Chemical formula K4[Fe(CN)6] gives Molar mass 368.345, Atoms in the formula 17.Source: 4 × 39.098 + 55.845 + 6 × 12.011 + 6 × 14.007 = 368.345 (CIAAW, https://ciaaw.org/abridged-atomic-weights.htm)
How it works
The molar mass of a compound is the sum of the standard atomic weights of its atoms, in grams per mole:
molar mass = Σ (number of atoms of the element × standard atomic weight of the element)
Then
- moles = mass in grams ÷ molar mass
- grams = moles × molar mass
- share of an element by mass = 100 × (its atoms × its atomic weight) ÷ molar mass
Reading the formula
- Element symbols start with a capital letter, followed by at most one small letter (Co is cobalt, CO is carbon and oxygen). A number after a symbol is its count; no number means 1. Counts cannot be 0.
- Round brackets ( ) and square brackets [ ] group atoms, and a number after the closing bracket multiplies the group: Ca(OH)2 has 1 Ca, 2 O, 2 H. Brackets must match.
- A dot (·, •, ⋅, . or *) starts a hydrate part; a number right after the dot multiplies that part: CuSO4·5H2O has 1 Cu, 1 S, 9 O, 10 H.
- A whole number before the formula multiplies all of it: 2H2O is 4 H and 2 O (36.030 g/mol).
- Subscript digits (H₂O) read like normal digits. Spaces are ignored anywhere, also inside a charge (Fe³ ⁺ is Fe³⁺).
- An electron alone (e, e-, e^- or e⁻, with or without a number in front) gives no answer: "Enter a chemical formula, not an electron."
- A charge at the end, written with a caret (Fe^3+, SO4^2-, OH^-) or in superscripts (Fe³⁺), is allowed; it does not change the molar mass (the electrons are not counted). A phase label at the end, (s), (l), (g) or (aq), is ignored.
- Anything else gives no answer with a message, for example: "Xx" is not an element symbol; element symbols start with a capital letter; the brackets do not match.
- An element with no standard atomic weight gives no answer: "Tc has no standard atomic weight (it has no stable isotopes), so the molar mass of this formula is not defined." The elements without one are Tc, Pm, Po, At, Rn, Fr, Ra, Ac, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Cn, Nh, Fl, Mc, Lv, Ts and Og.
What the calculator shows
- Molar mass in g/mol. The table’s weights have at most four decimals, so the sum is exact; it is shown with up to four decimals and no trailing zeros (18.015).
- Formula: the formula as read, with subscript digits, a raised dot for hydrates, and the leading multiplier if you typed one.
- Composition by mass: one part per element in the order it first appears, joined by "; ", each written
<symbol>: <atoms> × <atomic weight> = <mass part> g/mol (<share>%). Weights and parts drop trailing zeros (1.0080 shows as 1.008). The share is rounded half up to exactly three decimals. - Atoms in the formula: the total count of atoms, including a leading multiplier.
- Moles in the sample (from a mass) and Mass of the amount (from moles), each to 6 significant figures.
Standard atomic weights used (CIAAW abridged, 2024)
| Element | Weight | Element | Weight | Element | Weight | Element | Weight |
|---|---|---|---|---|---|---|---|
| H | 1.0080 | He | 4.0026 | Li | 6.94 | Be | 9.0122 |
| B | 10.81 | C | 12.011 | N | 14.007 | O | 15.999 |
| F | 18.998 | Ne | 20.180 | Na | 22.990 | Mg | 24.305 |
| Al | 26.982 | Si | 28.085 | P | 30.974 | S | 32.06 |
| Cl | 35.45 | Ar | 39.95 | K | 39.098 | Ca | 40.078 |
| Sc | 44.956 | Ti | 47.867 | V | 50.942 | Cr | 51.996 |
| Mn | 54.938 | Fe | 55.845 | Co | 58.933 | Ni | 58.693 |
| Cu | 63.546 | Zn | 65.38 | Ga | 69.723 | Ge | 72.630 |
| As | 74.922 | Se | 78.971 | Br | 79.904 | Kr | 83.798 |
| Rb | 85.468 | Sr | 87.62 | Y | 88.906 | Zr | 91.222 |
| Nb | 92.906 | Mo | 95.95 | Ru | 101.07 | Rh | 102.91 |
| Pd | 106.42 | Ag | 107.87 | Cd | 112.41 | In | 114.82 |
| Sn | 118.71 | Sb | 121.76 | Te | 127.60 | I | 126.90 |
| Xe | 131.29 | Cs | 132.91 | Ba | 137.33 | La | 138.91 |
| Ce | 140.12 | Pr | 140.91 | Nd | 144.24 | Sm | 150.36 |
| Eu | 151.96 | Gd | 157.25 | Tb | 158.93 | Dy | 162.50 |
| Ho | 164.93 | Er | 167.26 | Tm | 168.93 | Yb | 173.05 |
| Lu | 174.97 | Hf | 178.49 | Ta | 180.95 | W | 183.84 |
| Re | 186.21 | Os | 190.23 | Ir | 192.22 | Pt | 195.08 |
| Au | 196.97 | Hg | 200.59 | Tl | 204.38 | Pb | 207.2 |
| Bi | 208.98 | Th | 232.04 | Pa | 231.04 | U | 238.03 |
Worked examples by hand
Water, H2O. 2 × 1.0080 + 1 × 15.999 = 2.016 + 15.999 = 18.015 g/mol. Hydrogen is 2.016 ÷ 18.015 = 11.191% of the mass and oxygen 88.809%.
Glucose, C6H12O6. 6 × 12.011 + 12 × 1.0080 + 6 × 15.999 = 72.066 + 12.096 + 95.994 = 180.156 g/mol. 90 g of glucose is 90 ÷ 180.156 = 0.499567 mol.
Table salt, NaCl. 22.990 + 35.45 = 58.44 g/mol. 2 mol weighs 2 × 58.44 = 116.88 g.
Copper(II) sulfate pentahydrate, CuSO4·5H2O. Cu 63.546 + S 32.06 + 9 O × 15.999 (143.991) + 10 H × 1.0080 (10.08) = 249.677 g/mol.
Calcium hydroxide, Ca(OH)2. 40.078 + 2 × 15.999 + 2 × 1.0080 = 40.078 + 31.998 + 2.016 = 74.092 g/mol.
Potassium ferrocyanide, K4[Fe(CN)6]. 4 × 39.098 + 55.845 + 6 × 12.011 + 6 × 14.007 = 156.392 + 55.845 + 72.066 + 84.042 = 368.345 g/mol.
Other questions people ask
How do I calculate molar mass?
Multiply the atomic weight of each element by the number of its atoms in the formula and add the results. For water, H2O: 2 × 1.0080 + 1 × 15.999 = 18.015 g/mol.
What is the difference between molar mass and molecular weight?
They are the same number with different units. Molar mass is the mass of one mole in grams per mole (g/mol); molecular weight (relative molecular mass) has no unit. Glucose has a molar mass of 180.156 g/mol and a molecular weight of 180.156.
How do I convert grams to moles?
Divide the mass in grams by the molar mass. 90 g of glucose is 90 ÷ 180.156 = 0.4996 mol. To go the other way, multiply moles by the molar mass: 2 mol of NaCl is 2 × 58.44 = 116.88 g.
How do I write brackets, hydrates and charges?
Type brackets as in Ca(OH)2 or K4[Fe(CN)6]. For a hydrate, put a dot or a star before the water: CuSO4·5H2O or CuSO4*5H2O. A charge goes at the end after a caret, as in SO4^2-; it does not change the molar mass here.
Which atomic weights does the calculator use?
The abridged standard atomic weights published by the IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024 table, the values most periodic tables print. The full table is below.
Why is there no answer for technetium or plutonium?
Elements with no stable isotopes, such as technetium, promethium and most elements from polonium onward, have no standard atomic weight, because their atomic mass depends on the sample. Thorium, protactinium and uranium do have one.
Why does my textbook give a slightly different molar mass?
Some books round atomic weights differently, for example H as 1.01 or Cl as 35.5, or use older tables. The small differences add up in large molecules. This calculator uses the current CIAAW abridged values exactly.