Homarus gammarus is a large crustacean , with a body length up to 60 centimetres ( 24 in ) and weighing up to 5 – 6 kilograms ( 11 – 13 lb ) , although the lobsters caught in lobster pots are usually 23 – 38 cm ( 9 – 15 in ) long and weigh 0 @.@ 7 – 2 @.@ 2 kg ( 1 @.@ 5 – 4 @.@ 9 lb ) . Like other crustaceans , lobsters have a hard exoskeleton which they must shed in order to grow , in a process called ecdysis ( moulting ) . This may occur several times a year for young lobsters , but decreases to once every 1 – 2 years for larger animals .