Blue spruce is a medium-sized evergreen tree growing to 25–30 m tall, exceptionally to 46 m tall, and with a trunk diameter of up to 1.5 m. The bark is thin and scaly, flaking off in small circular plates 5–10 cm across. The crown is conic in young trees, becoming cylindric in older trees. The shoots are stout, orange-brown, usually glabrous, and with prominent pulvini.The leaves are needle-like, 15–30 mm long, stout, rhombic in cross-section, dull gray-green to bright glaucous blue (very variable from tree to tree in wild populations), with several lines of stomata ; the tip is viciously sharp. The cones are pendulous, slender cylindrical, 6–11 cm long and 2 cm broad when closed, opening to 4 cm broad. They have thin, flexible scales 20–24 mm long, with a wavy margin. They are reddish to violet, maturing pale brown 5–7 months after pollination. The seeds are black, 3–4 mm long, with a slender, 10–13 mm long pale brown wing.