Sucrose is 342.30 g/mol

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Sucrose has a molar mass of 342.30 g/mol and the formula C12H22O11, while glucose has a molar mass of 180.16 g/mol and the formula C6H12O6. The gap is not rounding: sucrose is built from glucose plus fructose, so its mass is roughly the sum of two monosaccharide units minus one molecule of water.

Common sugars by formula, molar mass, component units, bond type and glycaemic index.
Sugar	Formula
Glucose	C6H12O6
Fructose	C6H12O6
Galactose	C6H12O6
Sucrose	C12H22O11
Lactose	C12H22O11
Maltose	C12H22O11
Starch (polymer)	(C6H10O5)n
Cellulose (polymer)	(C6H10O5)n

Terms used on this page

Monosaccharide: A single sugar ring with the formula C6H12O6 and a molar mass of 180.16 g/mol. Glucose, fructose and galactose are the common examples.
Disaccharide: Two monosaccharide units joined by a glycosidic bond, with the formula C12H22O11 and a molar mass of 342.30 g/mol. Sucrose, lactose and maltose are the common examples.
Glycosidic bond: The link between two sugar units. Its geometry is described as alpha or beta, and that geometry decides whether human enzymes can split it.
Glycaemic index: A scale comparing the blood-glucose response to a sugar against glucose, which is set at 100. Sucrose is about 65 and fructose about 19.
Inverted sugar: The mixture of glucose and fructose produced when sucrose is hydrolysed. It rotates plane-polarised light by about −19 degrees, opposite in sign to intact sucrose at about +66 degrees.
Amylose: The linear fraction of starch, roughly 20–30% of the total, built with alpha-1,4 bonds. Amylopectin makes up the rest.

What is the molar mass of sucrose, and how does it differ from glucose?

Sucrose is 342.30 g/mol; glucose is 180.16 g/mol — a difference of 162.14 g/mol, close to one added monosaccharide unit minus water.

Sucrose carries the formula C12H22O11, which is what you read off the label when you want its molar mass. Twelve carbons, twenty-two hydrogens and eleven oxygens add up to 342.30 g/mol. Glucose carries C6H12O6, and the same arithmetic gives 180.16 g/mol.

The two numbers are not independent facts. Sucrose is glucose plus fructose joined by a glycosidic bond. When two monosaccharides condense, one water molecule (about 18.02 g/mol) leaves. Two glucose units at 180.16 g/mol each would be 360.32 g/mol before condensation; after losing water the disaccharide lands at 342.30 g/mol.

That is why the mass difference between a monosaccharide and a disaccharide in this family is roughly 162.14 g/mol, not a clean 180.16. The missing 18.02 is the water that was expelled when the bond formed. The same logic holds for lactose (glucose plus galactose) and maltose (glucose plus glucose).

For practical purposes, you rarely need the exact figure beyond two decimal places. What matters is the class: if a sugar reads 180.16 g/mol, it is a single ring; if it reads 342.30 g/mol, it is two rings joined.

Monosaccharides: C6H12O6, 180.16 g/mol — glucose, fructose, galactose.
Disaccharides: C12H22O11, 342.30 g/mol — sucrose, lactose, maltose.
Condensation removes one water molecule, about 18.02 g/mol.
Two monosaccharide units minus water gives the disaccharide mass.

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Reading a molar mass off the molecular formula

Count the atoms, multiply by atomic masses, and the formula gives you the molar mass without any lab work.

Carbon contributes about 12.011 g/mol per atom, hydrogen about 1.008, oxygen about 15.999. For C6H12O6 that is 6 × 12.011 + 12 × 1.008 + 6 × 15.999, which rounds to 180.16 g/mol. For C12H22O11 the same arithmetic yields 342.30 g/mol.

The formula also tells you which class you are looking at. Any sugar with six carbons, twelve hydrogens and six oxygens is a monosaccharide. Any sugar with twelve carbons, twenty-two hydrogens and eleven oxygens is a disaccharide. There is no third common formula in this set.

This is why glucose, fructose and galactose are isomers: same formula, same mass, different arrangement. And why sucrose, lactose and maltose are isomers of each other: same formula, same mass, different component sugars and different bonds.

Write the formula: C6H12O6 or C12H22O11.
Multiply each element count by its atomic mass.
Add the three products.
Round to two decimal places for the standard value.

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Alpha versus beta glycosidic bonds

Maltose and starch use an alpha-1,4 bond; lactose and cellulose use a beta-1,4 bond — and that one letter decides whether a human can digest it.

The bond between two sugar rings is called a glycosidic bond, and its geometry is described as alpha or beta. Maltose and starch are built with alpha-1,4 linkages. Lactose and cellulose are built with beta-1,4 linkages.

Human digestive enzymes are shaped to fit the alpha bond. They can cleave maltose and starch into glucose units. They cannot cleave the beta bond in cellulose, which is why cellulose passes through the human gut largely intact even though it is a glucose polymer just like starch.

Lactose is a special case: it is a disaccharide with a beta-1,4 bond between glucose and galactose, and many adults lose the enzyme needed to split it. The bond type is the same as in cellulose, but the molecule is small enough that a different enzyme handles it in those who still produce it.

Alpha-1,4: maltose, starch — digestible by human enzymes.
Beta-1,4: lactose, cellulose — lactose only if the enzyme is present; cellulose not at all.
Same formula, same mass, different geometry, different outcome.