The adult okapi weighs anywhere from 440 - 660 lbs., has a head-to-body length of 6.5 to almost 7 feet, and a shoulder height of 5 - 5.5 feet, with the females being larger on average than the males. Their bodies are short and compact with a spine that is approximately level, only slightly sloping downward from the neck to the hind legs, to a lesser degree than the spine of the giraffe.

The okapi's skull is what allows it to have a long, narrow muzzle, large eyes, large ears, and eventually, in males, ossicones. Male okapi are not born with ossicones, these horns start out as disks of cartilage under the skin, grow to shape during early development, then turn into bone and fuse to the underlying frontal bone of the skull once the male reaches maturity.

A large gap exists between the okapi's premolars, present at the back of its jaw, and its incisors, present at the very front of the skull and only on the lower jaw. The okapi strips leaves from various plants using these lower incisors and the upper palate portion of its mouth known as a dental pad.

The okapi possess cloven hooves, or two separate hooves on each foot, that surround what would be the third and fourth toe in other mammals. While it's neck is not as long as the giraffes, it is still longer than most other ungulates due to the stretching of the cervical vertebrae unique to the Giraffidae family. Among these other skeletal formations, the okapi has only 3 tarsal (ankle) bones compared to the giraffe's 4 along with 5 sacral vertebrae, more than the giraffe who only has 4.