Northern red oak is a large tree with a tall, straight trunk; large, spreading branches; and a rounded crown.
Leaves are alternate, simple, 5–9 inches long, with 7–11 bristle-tipped lobes cut halfway to the midrib. Lobes are uneven in size and length, those along the upper half short and broad. Upper surface smooth, yellow-green; lower surface smooth with occasional tufts at the intersection of the veins.
Bark is greenish-brown to gray, becoming brown to black with age. Grooves shallow, ridges wide, flat-topped, grayish bark appearing as stripes. Bark on upper trunk rough and shallow-fissured, with broad, smooth streaks; bark on lower trunk gray to black, deeply furrowed.
Twigs are slender, reddish-brown, slightly hairy at first, becoming smooth and shiny. Buds reddish, fringed with hair.
Flowers April–May, in catkins.
Fruits September–October, acorns, reddish-brown, shiny, 1–1¼ inches long, barrel-shaped, hairy at the cup end. Cup encloses about ¼ of the nut. Acorns ripen in autumn of second year.