Adults of H. leptonyx reach 241-338 cm in length, with females being on average slightly larger than males. The body is streamlined and massive, with a very large head and long, broad foreflippers. Leopard seals swim with long, powerful, simultaneous strokes of the forelimbs, unlike most other phocids which propel themselves by means of side-to-side strokes of the hindlimbs. Coloration is dark above giving way to silvery pale on the sides and below, with varying degrees of spotting. In addition to having well developed canines, the cheek teeth of the leopard seal consist of three tubercles or lobes, similar to those of the crabeater seal, Lobodon carcinophaga. These complex teeth allow the leopard seal to filter krill from the water.
Range mass: 200 to 591 kg.
Range length: 241 to 338 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: female larger