The molar mass of sucrose, C12H22O11, is 342.297 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 342.297 g, and a gram of it is 1.759e+21 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. Sucrose is 12 × 12.011 (C) + 22 × 1.008 (H) + 11 × 15.999 (O), which is 342.297 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Oxygen makes up the largest share of the mass: 11 of the 45 atoms in a formula unit are oxygen, and they account for 175.989 g of the 342.297 g, or 51.41% 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 sucrose is 342.297 mg and one micromole is 342.297 µg, so a balance reading to a milligram places you within 2.921 µmol. A single formula unit weighs 5.6840e-22 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
Table sugar, a disaccharide of glucose and fructose. Sugar solutions are quoted in degrees Brix, which is percent by weight rather than molarity. At 342.297 g/mol it is heavier than 19 of the 21 organic compounds covered here, and that ranking matters more than it looks: EDTA has a molar mass of 292.244 g/mol, so a gram of it contains 17.1% more formula units than a gram of sucrose. 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 6.8459 g of a nominal 342.297 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 sucrose in grams
342.297- The molar mass of sucrose 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 sucrose in grams.
- It is divided by the molar mass, 342.297 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 sucrose as a molecule count
0.5 g divided by 342.297 g/mol is 0.00146072 mol, and multiplying by the Avogadro constant gives 8.797e+20 formula units of sucrose. The same mass is 1.4607 mmol, which is the figure a reaction is actually planned in.
5 g of sucrose as a molecule count
5 g divided by 342.297 g/mol is 0.0146072 mol, and multiplying by the Avogadro constant gives 8.797e+21 formula units of sucrose. The same mass is 14.607 mmol, which is the figure a reaction is actually planned in.
50 g of sucrose as a molecule count
50 g divided by 342.297 g/mol is 0.146072 mol, and multiplying by the Avogadro constant gives 8.797e+22 formula units of sucrose. The same mass is 146.07 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 sucrose (C12H22O11)?
It is 342.297 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 12 × 12.011 (C) + 22 × 1.008 (H) + 11 × 15.999 (O). One mole of sucrose therefore weighs 342.297 g, and a gram of it is 2.9214 mmol.
What percentage of sucrose is oxygen?
51.41% by mass. Each formula unit contains 11 oxygen atoms contributing 175.989 g of the 342.297 g total, so 100 g of sucrose contains 51.41 g of oxygen and a kilogram contains 514.14 g of it.
How many molecules are in one gram of sucrose?
About 1.759e+21. One gram is 0.00292144 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 342.297.
How much does a single molecule of sucrose weigh?
5.6840e-22 g, which is 342.297 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 sucrose it is 342.297. Molar mass carries grams per mole: 342.297 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. Oxygen is quoted as 15.999 rather than a whole number for that reason, and the same applies to the other elements here, which is why sucrose comes out at 342.297 g/mol rather than 342.
Molar mass, composition and mole equivalents of sucrose
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 11 | 15.999 | 175.989 | 51.41% |
| Carbon (C) | 12 | 12.011 | 144.132 | 42.11% |
| Hydrogen (H) | 22 | 1.008 | 22.176 | 6.479% |
| Total — one mole of sucrose | 342.297 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 342.297 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000342297 | 0.342297 | 6.022e+17 |
| 10 µmol | 0.00342297 | 3.42297 | 6.022e+18 |
| 100 µmol | 0.0342297 | 34.2297 | 6.022e+19 |
| 1 mmol | 0.342297 | 342.297 | 6.022e+20 |
| 10 mmol | 3.42297 | 3422.97 | 6.022e+21 |
| 50 mmol | 17.1149 | 17,114.9 | 3.011e+22 |
| 100 mmol | 34.2297 | 34,229.7 | 6.022e+22 |
| 250 mmol | 85.5743 | 85,574.2 | 1.506e+23 |
| 500 mmol | 171.149 | 171,148 | 3.011e+23 |
| 750 mmol | 256.723 | 256,723 | 4.517e+23 |
| 1 mol | 342.297 | 342,297 | 6.022e+23 |
| 2 mol | 684.594 | 684,594 | 1.204e+24 |
| 5 mol | 1711.49 | 1711485.000000 | 3.011e+24 |
| 10 mol | 3422.97 | 3422970.000000 | 6.022e+24 |
Mass is the amount multiplied by 342.297 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 |
|---|---|---|---|
| Uric acid | C5H4N4O3 | 168.112 | 5.9484 |
| Glucose | C6H12O6 | 180.156 | 5.5507 |
| Aspirin | C9H8O4 | 180.159 | 5.5507 |
| Caffeine | C8H10N4O2 | 194.194 | 5.1495 |
| EDTA | C10H16N2O8 | 292.244 | 3.4218 |
| Sucrose (this page) | C12H22O11 | 342.297 | 2.9214 |
| Cholesterol | C27H46O | 386.664 | 2.5862 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.