The black-chinned hummingbird is 3.25 inches long. Adults are metallic green above and white below with green flanks. Their bill is long, straight and very slender. The adult male has a black face and chin, a glossy purple throat band and a dark forked tail. The female has a dark rounded tail with white tips and no throat patch; they are similar to female ruby-throated hummingbirds. Juvenile plumage is similar to that of adult females, but with buff margins on the dorsal feathers. Juvenile males may also possess purple feathers on their throats.