The yellow-legged gull is a large gull, though the size does vary, with the smallest females being scarcely larger than a common gull and the largest males being roughly the size of a great black-backed gull. They range in length from in total length, from in wingspan and from in weight. Among standard measurements, the wing chord is , the bill is and the tarsus is . Adults are externally similar to herring gulls but have yellow legs. They have a grey back, slightly darker than herring gulls but lighter than lesser black-backed gulls. They are much whiter-headed in autumn, and have more extensively black wing tips with few white spots, just as lesser black-backed. They have a red spot on the bill as adults, like the entire complex. There is a red ring around the eye like in the lesser black-backed gull but unlike in the herring gull which has a dark yellow ring.