The bold white spectacles of the Blue-headed Vireo are a good field mark. Black-capped Vireo also has white spectacles but it has a black, not gray, head. Yellow-throated and White-eyed Vireos have yellow spectacles. Plumbeous and Cassin's Vireos are duller without bright yellow flanks and have less contrast between the head and back. The Gray Vireo lacks spectacles and has faint wing bars.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.