The red-billed tropicbird measures on average, which includes the -long . Without them the tropicbird measures about . It has a wingspan of . In overall appearance it is tern-like in shape. Its plumage is white, with black wing tips, and a back that is finely barred in black. It has a black mask that extends up from just above the lores to the sides of its nape, with gray mottling usually seen near the nape and hindneck. The tail has black shaft streaks, as do tail streamers. The are white, with some black on the outermost primaries and tertials and occasionally with black markings on the flanks. The iris is blackish-brown, and the bill is red. The legs, base of the central toe, and parts of the outer toes are orange-yellow while the rest of the feet are black. Although the sexes are similar, the males are generally larger than females, with the tail streamers being around longer on the male than on the female.