The skull and skeleton of E. annectens are well-known.
Edward Drinker Cope estimated the length of one specimen as about 38 feet (12 m) long, with a skull 3.87 feet (1.18 m) long.
This body length estimate was later revised down to a length of 29 feet (8.8 m), although to be fair to Cope a dozen vertebrae, the hips, and thigh bones had been carried away by a stream cutting through the skeleton, and the tip of the tail was incomplete.
A second skeleton currently exhibited next to  Cope's specimen, but in a standing posture, is estimated at 30 feet (9.1 m) long, with its head 17 feet (5.2 m) above the ground.
The hip height of this specimen is estimated as approximately 2.1 metres (6.9 ft).
Other sources have estimated the length of E. annectens as approximately 12 metres (39 ft).
Most specimens are somewhat shorter, representing individuals that are not fully grown.
Two well-known mounted skeletons, USNM 2414 and YPM 2182, measure 8.00 meters (26.25 ft) long and 8.92 meters (29.3 ft) long, respectively.
E. annectens may have weighed about 6.6 metric tons (7.3 tons) when fully grown.
Recently-found specimens that are still under study at the Museum of the Rockies, namely MOR 1142 ("X-rex") and MOR 1609 ("Becky's Giant"), suggest that E. annectens may have reached lengths of over 15 m (49 ft) and massed over 10 tons, potentially making it one of the largest hadrosaurids.

The skull of E. annectens is known for its long, wide muzzle.
Cope compared this feature to that of a goose in side view, and to a short-billed spoonbill in top view.
The skull was longer and lower proportionally than in any other known hadrosaurid.
The toothless portion of the anterior mandible was relatively longer than in any hadrosaur.
The extreme length and breadth did not appear until an individual reached maturity, so many specimens lack the distinctive shape.
The bones surrounding the large openings for the nostrils formed deep pockets around the openings.
The eye sockets were rectangular and longer front to back than top to bottom, although this may have been exaggerated by postmortem crushing.
The skull roof was flat and lacked a bony crest, and the quadrate bone that formed the articulation with the lower jaw was distinctly curved.
The lower jaw was long and straight, lacking the downward curve seen in other hadrosaurids, and possessing a heavy ridge running its length.
The predentary was wide and shovel-like.
The ridge on the lower jaw may have reinforced the long, slender structure.

As mounted, the vertebral column of E. annectens includes twelve neck, twelve back, nine sacral, and at least thirty tail vertebrae.
The limb bones were longer and more lightly built than those of other hadrosaurids of comparable size.
E. annectens had a distinctive pelvis, based on the proportions and form of the pubis bone.
E. annectens, like other hadrosaurids, could move both on two legs and on four legs.
It probably preferred to forage for food on four legs, but ran on two.
Henry Fairfield Osborn used the skeletons in the American Museum of Natural History to portray both quadrupedal and bipedal stances for E. annectens.
The skull and skeleton of E. annectens are well-known. Edward Drinker Cope estimated the length of one specimen as about 38 feet (12 m) long, with a skull 3.87 feet (1.18 m) long. This body length estimate was later revised down to a length of 29 feet (8.8 m), although to be fair to Cope a dozen vertebrae, the hips, and thigh bones had been carried away by a stream cutting through the skeleton, and the tip of the tail was incomplete. A second skeleton currently exhibited next to  Cope's specimen, but in a standing posture, is estimated at 30 feet (9.1 m) long, with its head 17 feet (5.2 m) above the ground. The hip height of this specimen is estimated as approximately 2.1 metres (6.9 ft). Other sources have estimated the length of E. annectens as approximately 12 metres (39 ft). Most specimens are somewhat shorter, representing individuals that are not fully grown. Two well-known mounted skeletons, USNM 2414 and YPM 2182, measure 8.00 meters (26.25 ft) long and 8.92 meters (29.3 ft) long, respectively. E. annectens may have weighed about 6.6 metric tons (7.3 tons) when fully grown. Recently-found specimens that are still under study at the Museum of the Rockies, namely MOR 1142 ("X-rex") and MOR 1609 ("Becky's Giant"), suggest that E. annectens may have reached lengths of over 15 m (49 ft) and massed over 10 tons, potentially making it one of the largest hadrosaurids.
The skull of E. annectens is known for its long, wide muzzle. Cope compared this feature to that of a goose in side view, and to a short-billed spoonbill in top view. The skull was longer and lower proportionally than in any other known hadrosaurid. The toothless portion of the anterior mandible was relatively longer than in any hadrosaur. The extreme length and breadth did not appear until an individual reached maturity, so many specimens lack the distinctive shape. The bones surrounding the large openings for the nostrils formed deep pockets around the openings. The eye sockets were rectangular and longer front to back than top to bottom, although this may have been exaggerated by postmortem crushing. The skull roof was flat and lacked a bony crest, and the quadrate bone that formed the articulation with the lower jaw was distinctly curved. The lower jaw was long and straight, lacking the downward curve seen in other hadrosaurids, and possessing a heavy ridge running its length. The predentary was wide and shovel-like. The ridge on the lower jaw may have reinforced the long, slender structure.
As mounted, the vertebral column of E. annectens includes twelve neck, twelve back, nine sacral, and at least thirty tail vertebrae. The limb bones were longer and more lightly built than those of other hadrosaurids of comparable size. E. annectens had a distinctive pelvis, based on the proportions and form of the pubis bone. E. annectens, like other hadrosaurids, could move both on two legs and on four legs. It probably preferred to forage for food on four legs, but ran on two. Henry Fairfield Osborn used the skeletons in the American Museum of Natural History to portray both quadrupedal and bipedal stances for E. annectens.
Edmontosaurus annectens