The molar mass of ethanol, C2H6O, is 46.069 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 46.069 g, and a gram of it is 1.307e+22 formula units. The calculator turns any weighed mass into that count, and reports the amount in moles, millimoles and the mass of a single formula unit alongside it.
The figure comes from the formula. Ethanol is 2 × 12.011 (C) + 6 × 1.008 (H) + 15.999 (O), which is 46.069 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Carbon makes up the largest share of the mass: 2 of the 9 atoms in a formula unit are carbon, and they account for 24.022 g of the 46.069 g, or 52.14% by mass. The derivation table below breaks the whole molecule down element by element.
The numbers a bench actually uses sit at the millimole scale. One millimole of ethanol is 46.069 mg and one micromole is 46.069 µg, so a balance reading to a milligram places you within 21.71 µmol. A single formula unit weighs 7.6499e-23 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
Drinking alcohol and a solvent. Strength is quoted as percent by volume, and because ethanol is less dense than water that is not percent by weight. At 46.069 g/mol it is heavier than 1 of the 21 organic compounds covered here, and that ranking matters more than it looks: methanol has a molar mass of 32.042 g/mol, so a gram of it contains 43.8% more formula units than a gram of ethanol. Weigh by mass and you are not weighing equal amounts of substance.
Two practical things move the result. Purity below 100% means the weighed mass overstates how much compound you have — at 98% assay, 0.92138 g of every 46.069 g is not the compound — and any water picked up from the air does the same. Both are systematic, so they shift every solution made from that jar in the same direction.
The formula
m- The mass of ethanol in grams
46.069- The molar mass of ethanol in g/mol, derived from its formula
N- The number of formula units that mass contains
How it works, step by step
- Enter a mass of ethanol in grams.
- It is divided by the molar mass, 46.069 g/mol, giving the amount in moles.
- That amount is multiplied by the Avogadro constant, 6.02214076 × 10²³ per mole, to give the number of formula units.
- The panel also reports the amount in moles and millimoles and the mass of one formula unit.
Worked examples
0.5 g of ethanol as a molecule count
0.5 g divided by 46.069 g/mol is 0.0108533 mol, and multiplying by the Avogadro constant gives 6.536e+21 formula units of ethanol. The same mass is 10.853 mmol, which is the figure a reaction is actually planned in.
5 g of ethanol as a molecule count
5 g divided by 46.069 g/mol is 0.108533 mol, and multiplying by the Avogadro constant gives 6.536e+22 formula units of ethanol. The same mass is 108.53 mmol, which is the figure a reaction is actually planned in.
50 g of ethanol as a molecule count
50 g divided by 46.069 g/mol is 1.08533 mol, and multiplying by the Avogadro constant gives 6.536e+23 formula units of ethanol. The same mass is 1085.3 mmol, which is the figure a reaction is actually planned in.
How to read your score
Frequently asked questions
What is the molar mass of ethanol (C2H6O)?
It is 46.069 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 2 × 12.011 (C) + 6 × 1.008 (H) + 15.999 (O). One mole of ethanol therefore weighs 46.069 g, and a gram of it is 21.707 mmol.
What percentage of ethanol is carbon?
52.14% by mass. Each formula unit contains 2 carbon atoms contributing 24.022 g of the 46.069 g total, so 100 g of ethanol contains 52.14 g of carbon and a kilogram contains 521.44 g of it.
How many molecules are in one gram of ethanol?
About 1.307e+22. One gram is 0.0217066 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 46.069.
How much does a single molecule of ethanol weigh?
7.6499e-23 g, which is 46.069 daltons. It is the molar mass divided by the Avogadro constant, and the number in daltons is numerically the same as the molar mass in g/mol — that equivalence is what makes the mole convenient.
Is molar mass the same as molecular weight?
They are the same number in ordinary use but not the same quantity. Molecular weight, properly relative molecular mass, is a ratio and has no unit: for ethanol it is 46.069. Molar mass carries grams per mole: 46.069 g/mol. Because the mole is defined so those agree, you can read one off the other.
Why is the molar mass not a whole number?
Because standard atomic weights are averages over the isotopes found in nature. Carbon is quoted as 12.011 rather than a whole number for that reason, and the same applies to the other elements here, which is why ethanol comes out at 46.069 g/mol rather than 46.
Molar mass, composition and mole equivalents of ethanol
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 2 | 12.011 | 24.022 | 52.14% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 34.73% |
| Hydrogen (H) | 6 | 1.008 | 6.048 | 13.13% |
| Total — one mole of ethanol | 46.069 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 46.069 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000046 | 0.046069 | 6.022e+17 |
| 10 µmol | 0.00046069 | 0.46069 | 6.022e+18 |
| 100 µmol | 0.0046069 | 4.6069 | 6.022e+19 |
| 1 mmol | 0.046069 | 46.069 | 6.022e+20 |
| 10 mmol | 0.46069 | 460.69 | 6.022e+21 |
| 50 mmol | 2.30345 | 2303.45 | 3.011e+22 |
| 100 mmol | 4.6069 | 4606.9 | 6.022e+22 |
| 250 mmol | 11.5173 | 11,517.2 | 1.506e+23 |
| 500 mmol | 23.0345 | 23,034.5 | 3.011e+23 |
| 750 mmol | 34.5517 | 34,551.8 | 4.517e+23 |
| 1 mol | 46.069 | 46,069 | 6.022e+23 |
| 2 mol | 92.138 | 92,138 | 1.204e+24 |
| 5 mol | 230.345 | 230,345 | 3.011e+24 |
| 10 mol | 460.69 | 460,690 | 6.022e+24 |
Mass is the amount multiplied by 46.069 g/mol. The last column is that amount multiplied by the Avogadro constant, 6.02214076 × 10²³ per mole.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Methanol | CH4O | 32.042 | 31.209 |
| Ethanol (this page) | C2H6O | 46.069 | 21.707 |
| Acetone | C3H6O | 58.08 | 17.218 |
| Urea | CH4N2O | 60.056 | 16.651 |
| Isopropyl alcohol | C3H8O | 60.096 | 16.64 |
| Ethylene glycol | C2H6O2 | 62.068 | 16.111 |
| Glycine | C2H5NO2 | 75.067 | 13.321 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.