The House Sparrow is a chunky bird, typically about 16 centimetres (6.3 in) long, ranging from 14–18 centimetres (5.5–7.1 in). It has a large rounded head, a short tail, and a stout bill. In weight, the House Sparrow generally ranges from 24–39.5 grams (0.85–1.39 oz). Weight varies by sex, with females usually smaller than males. Younger birds are smaller, males are larger during the winter, and females larger during the breeding season. Between and within subspecies, there is further variation based on latitude, altitude, climate, and other environmental factors, under biological rules such as Bergmann's rule.
The plumage of the House Sparrow is mostly different shades of grey and brown. The sexes differ, with females and juveniles mostly buff, and the male marked with bold colours. The male is duller in fresh non-breeding plumage, with buff tips on many feathers. Wear and preening expose bright markings of brown and black, including a throat and chest patch, called a "bib" or a "badge". This patch is variable in width and general size, and some scientists have suggested that patches signal social status or fitness, a hypothesis which has led to a "veritable 'cottage industry'" of studies, which have only conclusively shown that patches increase in size with age. In breeding plumage, the male's crown is grey, and it is marked with black on its throat and beneath its crown. The cheeks and underparts are pale grey. The mantle and upper back are a warm brown, broadly streaked with black, while the lower back, rump and uppertail coverts are a greyish-brown. The female has no black on head or throat, nor a grey crown and its upperparts are streaked with brown. The juvenile is deeper brown, and the white is replaced by buff; the beak is pink to dull yellow.
There is some variation in the twelve subspecies of House Sparrow. The subspecies are divided into two groups, the Oriental indicus group, and the Palaearctic domesticus group. Birds of the domesticus group have grey cheeks, while indicus group birds have white cheeks, as well as bright colouration on the crown, a smaller bill, and a longer black bib. The subspecies Passer domesticus tingitanus differs little from the nominate subspecies, except in the worn breeding plumage of the male, in which the head is speckled with black and underparts are paler. P. d. balearoibericus is slightly paler than the nominate but darker than P. d. bibilicus. P. d. bibilicus is paler than most subspecies, but has the grey cheeks of domesticus group birds. The similar P. d. persicus is paler and smaller, and P. d. niloticus is nearly identical but smaller. Of the less wide ranging indicus group subspecies, P. d. hyrcanus is larger than P. d. indicus, P. d. bactrianus is larger and paler,P. d. parkini is larger and darker with more black on the breast than any other subspecies, and P. d. hufufae is paler.
The House Sparrow can be confused with a number of other seed-eating birds, especially its relatives in the genus Passer. Many of these relatives are smaller, with an appearance that is neater or "cuter", as with the Dead Sea Sparrow. The dull-coloured female often can not be distinguished from other birds, and it is nearly identical to the females of the Spanish Sparrow and Italian Sparrow. The Eurasian Tree Sparrow is smaller and more slender with a chestnut crown and a black patch on each cheek. The male Spanish Sparrow and Italian Sparrow are distinguished by their chestnut crowns. The Sind Sparrow is smaller, with the male less black on the throat and the female usually having a distinct pale supercilium.
