In the northern part of its range, black oak is a relatively small tree, reaching a height of 20–25 m (66–82 ft) and a diameter of 90 cm (35 in), but it grows larger in the south and center of its range, where heights of up to 42 m (138 ft) are known. Black oak is well known to readily hybridize with other members of the red oak (Quercus sect. Lobatae) group, being one parent in at least a dozen different named hybrids.
The leaves of the black oak are alternately arranged on the twig and are 10–20 cm (4–8 in) long with 5–7 bristle-tipped lobes separated by deep U-shaped notches. The upper surface of the leaf is a shiny deep green, the lower is yellowish-brown. There are also stellate hairs on the underside of the leaf that grow in clumps. Some key characteristics for identification include that leaves grown in the sun have very deep u-shaped sinuses and that the buds are velvety and covered in white hair.