A glucose molecule is a single unit of glucose, the most common simple sugar and an important source of energy for living things. It is about 0.8 nanometers across, measured by how it moves through water. A nanometer is a billionth of a meter. Each molecule is built from 24 atoms: 6 of carbon, 12 of hydrogen and 6 of oxygen, written C₆H₁₂O₆.

Size

A glucose molecule is not round, and like any molecule it has no hard edge, so its size depends on how it is measured. In water, glucose is usually shaped like a ring. The ring has six corners, and neighboring carbon atoms in it are about 0.15 nanometers apart. Measured along its longest direction, the whole molecule is roughly 1 nanometer long.

Another measure comes from how glucose moves through water. Tests of how much glucose thickens water give it a radius of 0.42 nanometers. That figure includes the water molecules that cling to it as it moves. It makes the molecule about 0.84 nanometers across, close to the explorer's 0.8 nanometers.

Size comparisons

About 100,000–125,000 glucose molecules side by side would span a human hair, which is 0.08–0.1 millimeters wide.
A glucose molecule is 10 times as heavy as a water molecule, and about three times as wide.
If a glucose molecule were enlarged to the size of a basketball, a human hair 0.1 millimeters wide would be about 30 kilometers (19 miles) wide.
A single chain of cellulose, the main material of wood and paper, is made of hundreds to thousands of glucose molecules linked in a line.

What glucose does

Plants make glucose from carbon dioxide and water, and use it to meet their energy needs. Animals that eat plants get much of their glucose by breaking down starch, the form in which plants store sugar. Inside cells, energy released from glucose is used to make ATP, a molecule that cells use to carry energy.

Humans and other animals with backbones store extra glucose as glycogen, mostly in the liver and muscles. When the level of glucose in the blood falls, the body breaks glycogen down to release glucose again.

Chains of glucose

Starch, glycogen and cellulose are all long chains of glucose molecules. Cellulose makes up most of the walls of plant cells. It is the most common natural polymer, a giant molecule built from repeating units.

Human digestive enzymes cannot break the links between the glucose units in cellulose, so people cannot digest it. Cows, koalas and some other plant-eating animals can, with the help of microbes in their stomachs. Table sugar is a different sugar, sucrose, made of one glucose unit joined to one fructose unit.

Sources

How big are biochemical nuts and bolts?. In Cell Biology by the Numbers, by Ron Milo and Rob Phillips. Garland Science, 2015.
Probing the Geometry of the Inner Vestibule of BK Channels with Sugars. Brelidze and Magleby, Journal of General Physiology, 2005.
Carbohydrates. In Biology 2e. OpenStax, 2018.
Just How Small Is "Nano"?. National Nanotechnology Initiative.
Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.

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