House finches are sparrow-sized birds. Males are reddish with heavy, brown streaks. Females are brown birds with heavy brown streaks on white underparts. House finches differ from purple finches by the male purple finch's purple side streaks (unlike the brown streaks in a house finch) and by the female's conspicuous eye stripe (female house finches lack this feature.) In the Black Hills, house finches could be confused with Cassin's finches, but the house finch has much heavier ventral streaking and lacks the Cassin's finch's back streaking. Female house finches are harder to distinguish, but are generally less boldly patterned.
House finches owe their red color to carotenoid pigments in their food; occasionally you may see yellow or orange individuals, if their diet lacks these pigments. Female house finches, however, prefer to mate with the reddest males they can find.