One glucose molecule contains six carbon atoms. Its molecular formula is C6H12O6, and its six-carbon framework is why glucose is classified as a hexose, more specifically an aldohexose.
Glucose is a monosaccharide, meaning it is a single-unit sugar rather than a carbohydrate built from multiple sugar units. Plants produce glucose from carbon dioxide and water using light energy during photosynthesis. The glucose can then be converted into starch for storage or used to build cellulose, the structural material of plant cell walls.
A common visual mistake comes from glucose’s ring form. In water, most glucose molecules exist as cyclic structures in which one oxygen atom is part of the ring, but the molecule still contains six carbon atoms. Glucose is also called dextrose in many commercial and medical contexts, and animals use it as a major fuel for producing ATP. Its six-carbon structure is retained even when glucose is joined to other sugars or assembled into polymers such as glycogen and starch.