Males unmistakable when red crown is seen but beware of poor lighting conditions. Females and immatures are fairly large and gray breasted, and often show the distinctive rosy-red gorget color on the throat. Costa's and the two Archilochus hummingbirds are the most likely identification contenders, but are smaller with whiter breasts and different call notes.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.