It depends on the type of seal. There are 18 species of true seals, according to Seals World. The largest is the southern elephant seal. Males are massive, weighing up to 8,500 lbs. (3,855.5 kilograms). Females are much smaller, but still weigh more than a car at 2,000 lbs. (907.18 kg). The smallest is the ringed seal, with an average length of 5 feet (1.5 m) and a weight of 110 to 150 lbs.