Quercus macrocarpa is a large deciduous tree growing up to 98 ft (30 m), rarely 160 ft (50 m), in height, and is one of the most massive oaks with a trunk diameter of up to 10 ft (3 m); reports of taller trees occur, but have not been verified. It is one of the slowest-growing oaks, with a growth rate of 1 ft (30 cm) per year when young. However, other sources state that a bur oak tree that is planted in the ground grows up to 3 ft (91 cm) per year. A 20-year-old tree will be about 60 ft (18 m) tall if grown in full sun. Naturally occurring saplings in forests will typically be older. Bur oaks commonly get to be 200 to 300 years old, and may live up to 400 years. The bark is gray with distinct vertical ridges.
The leaves are 2+3⁄4–6 in (7–15 cm) long and 2–5 in (5–13 cm) broad, variable in shape, with a lobed margin. Most often, the basal two-thirds is narrower and deeply lobed, while the apical third is wider and has shallow lobes or large teeth. They usually do not show strong fall color, although fine golden hues are occasionally seen. The flowers are greenish-yellow catkins, produced in the spring. The acorns are very large, 1–2 in (2.5–5 cm) long and 3⁄4–1+1⁄2 in (2–4 cm) broad, having a large cup that wraps much of the way around the nut, with large overlapping scales and often a fringe at the edge of the cup.
The wood when sawn transversely shows the characteristic annual rings formed by secondary thickening.
Bur oak is sometimes confused with other members of the white oak section, such as Quercus bicolor (swamp white oak), Quercus lyrata (overcup oak), and Quercus alba (white oak). It hybridizes with several other species of oaks.