Castanea dentata is a rapidly-growing, large, deciduous hardwood dicot tree. Pre-blight sources give a maximum height of 115 feet (35 m), and a maximum circumference of 13 feet (4.0 m). Post-blight sources erroneously report a greater maximum size of the species compared with pre-blight, likely due to nostalgia, to interpretations of pre-blight measurements of circumference as being measurements of diameter, and to the misapprehension that pre-blight observations of maximum size represented observations of average size. It is considerably larger than the closely related Allegheny chinquapin (Castanea pumila).

There are several other chestnut species, such as the European sweet chestnut (C. sativa), Chinese chestnut (C. mollissima), and Japanese chestnut (C. crenata). Castanea dentata can be distinguished by a few morphological traits, such as petiole length, nut size and number of nuts per burr, leaf shape, and leaf size, with leaves being 14–20 cm (5.5–8 in) long and 7–10 cm (3–4 in) broad—slightly shorter and broader than the sweet chestnut. It has larger and more widely spaced saw-teeth on the edges of its leaves, as indicated by the scientific name dentata, Latin for "toothed".

The European sweet chestnut was introduced in the United States by Thomas Jefferson in 1773. The European sweet chestnut has hairy twig tips in contrast to the hairless twigs of the American chestnut. This species has been the chief source of commercial chestnuts in the United States. Japanese chestnut was inadvertently introduced into the United States by Thomas Hogg in 1876 and planted on the property of S. B. Parsons in Flushing, New York. The Japanese chestnut has narrow leaves, smaller than either American chestnut or sweet chestnut, with small, sharply-pointed teeth and many hairs on the underside of the leaf and is the most blight-resistant species.

The chestnut is monoecious, and usually protandrous producing many small, pale green (nearly white) male flowers found tightly occurring along 6 to 8 inch long catkins. The female parts are found near the base of the catkins (near twig) and appear in late spring to early summer. Like all members of the family Fagaceae, American chestnut is self-incompatible and requires two trees for pollination, which can be with other members of the Castanea genus. The pollen of the American chestnut is considered a mild allergen.

The American chestnut is a prolific bearer of nuts, beginning inflorescence and nut production in the wild when a tree is 8 to 10 years old. American chestnut burrs often open while still attached to the tree, around the time of the first frost in autumn, with the nuts then falling to the ground. American chestnut typically have three nuts enclosed in a spiny, green burr, each lined in a tan velvet. In contrast, the Allegheny chinquapin produces but one nut per burr.