The trees reach a height of 30–35 m (98–115 ft) with a diameter of 0.4–1.5 m (1.3–4.9 ft). Exceptional specimens may reach 50 m (160 ft) tall, the largest of the southern pines. The seed cones are green, ripening pale buff-brown, 7–13 cm (2.8–5.1 in) in length, 2–3 cm (0.79–1.2 in) broad when closed, opening to 4–6 cm (1.6–2.4 in) wide, each scale bearing a sharp 3–6 mm spine.
The word loblolly means "low, wet place", but these trees are not limited to that specific habitat. Loblolly pines grow well in acidic clay soil, which is common throughout the South US, and are thus often found in large stands in rural places.
The tallest loblolly pine currently known, in Congaree National Park, is 51.4 m (169 ft) tall, and the largest, also in Congaree National Park, is 42 cubic meters in volume. A study using loblolly pines showed that higher atmospheric carbon dioxide levels may help the trees to endure ice storms better.