Firs are large trees, reaching heights of 10–80 metres (33–262 feet) tall with trunk diameters of 0.5–4 m (1 ft 8 in – 13 ft 1 in) when mature. Firs can be distinguished from other members of the pine family by the way in which their needle-like leaves are attached singly to the branches with a base resembling a suction cup, and by their cones, which, like those of true cedars, stand upright on the branches like candles and disintegrate at maturity.
Decay resistance helps this species live to great age; trees 600-800 years old are not uncommon in certain parts of its range with long fire return intervals. Trees 1,000 years or older have been recorded from several parts of its range, including several individuals between 1,300 and 1,400 years old.
One acre of Fir trees can give off the amount of oxygen needed for 18 people. This same acre of Fir trees will take in around 500 pounds of carbon dioxide annually.