3 Boil lobsters for 12 to 20 min, depending on size: Note the time at which the water comes to a boil again. From that point, boil the lobsters for 12-20 minutes or longer, depending on the size of the lobster. 12-15 minutes for 1 lb lobster, 15-20 minutes for a 1 1/2 pound lobster, 20-25 minutes for a 2-3 pound lobster. The lobsters should be a bright vivid red color when done.