Breeding adult Common Sandpipers have brownish-gray heads, napes, and breasts, all faintly streaked with dark brown. Their bellies and undertail coverts are plain white. The back, wings, and tail are darker brown, mottled with shades of tan and dark brown. They often have a white eye ring. After breeding, they molt into a drabber winter plumage with reduced or absent streaking. Juveniles have white speckles on their upper parts and look similar to winter adults but with more buff in their mottled upper parts. This species is distinguishable from the Spotted Sandpiper by its longer tail feathers and darker legs. At hatching, they weigh about 8 grams, increasing to around 40 grams when able to fly. They grow to about 20 cm in length, with a bill length of 21 mm and a wingspan of 35 cm. There is no sexual dimorphism in plumage, but females are typically slightly larger than males.