In accordance with its common name, L. ridibundus is distinguished by its dark brown or grayish-black frontal hood. Its eye crescents (primarily behind the eye), neck, and underparts are all white as is the tail. The upper wing coverts, secondaries, inner primaries, and back are gray. The secondaries are tipped with white; the white outer primaries have black tips and edges. Other identifying characteristics of L. ridibundus include its red legs and bill, and dark brown eyes. Non-breeding adults have a white head, with only some blackish coloring on their nape. Juvenile birds are recognized by the beige to darker brown markings on their back and upper wing coverts. Also, they have a black terminal tail band. The species is sexually monomorphic. Larus ridibundus ranges from 37 to 43 cm in length and has a wingspan from 94 to 110 cm (Howard and Moore, 1991).
Range mass: 195 to 325 g.