Individuals of the Styracosaurus genus were approximately 5.5 m (18 ft) long as adults and weighed around 2.7 tons. The skull was massive, with a large nostril, a tall straight nose horn, and a parietosquasomal frill (a neck frill) crowned with at least four large spikes. Each of the four longest frill spines was comparable in length to the nose horn, at 50 to 55 centimeters long (19.7 to 21.7 in). The nasal horn is estimated at 57 centimeters long (19.7 in) in the type specimen, but the horn is only partially complete. Based on other nasal horn cores from Styracosaurus and Centrosaurus, this horn may have come to a rounded point at around half of that length.
Aside from the large nasal horn and four long frill spikes, the cranial ornamentation was variable. Some individuals had small hook-like projections and knobs at the posterior margin of the frill, similar to but smaller than those in Centrosaurus. Others had less prominent tabs. Some, like the type individual, had a third pair of long frill spikes. Others had much smaller projections. Second species S. ovatus had only four large spikes, but the inner pair curved toward each other, the opposite of what is seen in the much better known S. albertensis. Other small points are found on the side margins of some but not all specimens. Modest pyramid-shaped brow horns were present in subadults, but were replaced by pits in adults. Like most ceratopsids, Styracosaurus had large fenestrae (skull openings) in its frill. The front of the mouth had a toothless beak
The bulky body of Styracosaurus resembled that of a rhinoceros. It had powerful shoulders which may have been useful in intraspecies combat. Styracosaurus had a relatively short tail. Each toe bore a hooflike ungual which was sheathed in horn.
Various limb positions have been proposed for Styracosaurus and ceratopsids in general, including forelegs which were held underneath the body, or, alternately, held in a sprawling position. The most recent work has put forward an intermediate crouched position as most likely. Paleontologists Gregory Paul and Per Christiansen of the Zoological Museum of the University of Copenhagen in Denmark proposed that large ceratopsians such as Styracosaurus were able to run at speeds exceeding that of an elephant, based on possible ceratopsian trackways which did not exhibit signs of sprawling forelimbs.