The molar mass of isopropyl alcohol, C3H8O, is 60.096 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 60.096 g, and a gram of it is 1.002e+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. Isopropyl alcohol is 3 × 12.011 (C) + 8 × 1.008 (H) + 15.999 (O), which is 60.096 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: 3 of the 12 atoms in a formula unit are carbon, and they account for 36.033 g of the 60.096 g, or 59.96% 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 isopropyl alcohol is 60.096 mg and one micromole is 60.096 µg, so a balance reading to a milligram places you within 16.64 µmol. A single formula unit weighs 9.9792e-23 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
Rubbing alcohol, sold at 70% for disinfection and 99% for electronics. The 70% strength is the more effective disinfectant, not the weaker one. At 60.096 g/mol it is heavier than 4 of the 21 organic compounds covered here, and that ranking matters more than it looks: urea has a molar mass of 60.056 g/mol, so a gram of it contains 0.0666% more formula units than a gram of isopropyl alcohol. Weigh by mass and you are not weighing equal amounts of substance.
Purity is the usual gap between the calculation and the balance. A reagent sold at 98% means 1.2019 g of a nominal 60.096 g is something else, so for exact work you divide the weighed mass by the assay figure on the certificate. For most purposes the difference is smaller than the error in reading the meniscus, but it is systematic rather than random, so it does not average out.
The formula
m- The mass of isopropyl alcohol in grams
60.096- The molar mass of isopropyl alcohol 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 isopropyl alcohol in grams.
- It is divided by the molar mass, 60.096 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 isopropyl alcohol as a molecule count
0.5 g divided by 60.096 g/mol is 0.00832002 mol, and multiplying by the Avogadro constant gives 5.01e+21 formula units of isopropyl alcohol. The same mass is 8.32 mmol, which is the figure a reaction is actually planned in.
5 g of isopropyl alcohol as a molecule count
5 g divided by 60.096 g/mol is 0.0832002 mol, and multiplying by the Avogadro constant gives 5.01e+22 formula units of isopropyl alcohol. The same mass is 83.2 mmol, which is the figure a reaction is actually planned in.
50 g of isopropyl alcohol as a molecule count
50 g divided by 60.096 g/mol is 0.832002 mol, and multiplying by the Avogadro constant gives 5.01e+23 formula units of isopropyl alcohol. The same mass is 832 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 isopropyl alcohol (C3H8O)?
It is 60.096 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 3 × 12.011 (C) + 8 × 1.008 (H) + 15.999 (O). One mole of isopropyl alcohol therefore weighs 60.096 g, and a gram of it is 16.64 mmol.
What percentage of isopropyl alcohol is carbon?
59.96% by mass. Each formula unit contains 3 carbon atoms contributing 36.033 g of the 60.096 g total, so 100 g of isopropyl alcohol contains 59.96 g of carbon and a kilogram contains 599.59 g of it.
How many molecules are in one gram of isopropyl alcohol?
About 1.002e+22. One gram is 0.01664 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 60.096.
How much does a single molecule of isopropyl alcohol weigh?
9.9792e-23 g, which is 60.096 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 isopropyl alcohol it is 60.096. Molar mass carries grams per mole: 60.096 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 isopropyl alcohol comes out at 60.096 g/mol rather than 60.
Molar mass, composition and mole equivalents of isopropyl alcohol
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 3 | 12.011 | 36.033 | 59.96% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 26.62% |
| Hydrogen (H) | 8 | 1.008 | 8.064 | 13.42% |
| Total — one mole of isopropyl alcohol | 60.096 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 60.096 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000060 | 0.060096 | 6.022e+17 |
| 10 µmol | 0.00060096 | 0.60096 | 6.022e+18 |
| 100 µmol | 0.0060096 | 6.0096 | 6.022e+19 |
| 1 mmol | 0.060096 | 60.096 | 6.022e+20 |
| 10 mmol | 0.60096 | 600.96 | 6.022e+21 |
| 50 mmol | 3.0048 | 3004.8 | 3.011e+22 |
| 100 mmol | 6.0096 | 6009.6 | 6.022e+22 |
| 250 mmol | 15.024 | 15,024 | 1.506e+23 |
| 500 mmol | 30.048 | 30,048 | 3.011e+23 |
| 750 mmol | 45.072 | 45,072 | 4.517e+23 |
| 1 mol | 60.096 | 60,096 | 6.022e+23 |
| 2 mol | 120.192 | 120,192 | 1.204e+24 |
| 5 mol | 300.48 | 300,480 | 3.011e+24 |
| 10 mol | 600.96 | 600,960 | 6.022e+24 |
Mass is the amount multiplied by 60.096 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 |
|---|---|---|---|
| Ethanol | C2H6O | 46.069 | 21.707 |
| Acetone | C3H6O | 58.08 | 17.218 |
| Urea | CH4N2O | 60.056 | 16.651 |
| Isopropyl alcohol (this page) | C3H8O | 60.096 | 16.64 |
| Ethylene glycol | C2H6O2 | 62.068 | 16.111 |
| Glycine | C2H5NO2 | 75.067 | 13.321 |
| Benzene | C6H6 | 78.114 | 12.802 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.