The Java sparrow is about 15 to 17 cm (5.9 to 6.7 in) in length from the beak to its tip of tail feathers. Although only about the size of a house sparrow, it may be the largest species in the estrildid family. The mean body mass is 24.5 g (0.86 oz), making it slightly heavier than its nearest known rival, the black-bellied seedeater. The adult is unmistakable, with its grey upperparts and breast, pink belly, white-cheeked black head, red eye-ring, pink feet and thick red bill.Both sexes are similar. Immature birds have brown upperparts and pale brown underparts, and a plain head. Very young birds have a black beak with a pink base.