Like most Vireos, the blue-headed vireo is a relatively small bird with a length of . The wingspan is usually found to be around and their weight is typically . There are some subtle differences between the "V.s. solitarius" and "V.s. alticola" subspecies. "V.s. alticola", the larger of the two subspecies, has a darker back with a larger wing length of and a bill length of . Conversely, "V.s. solitarius" is slightly smaller with a wing length of , and a bill length of .