Largest mammal
Who
Blue whale
What
190 tonne(s)/metric ton(s)
Where
United Kingdom (Southern Ocean,Antarctica)
When
Not applicable

The largest animal on Earth based on weight is the blue whale (Balaenoptera musculus), which can weigh up to 160 tonnes (352,739 lb). Its average length is 24 m (80 ft), but it is not the longest animal on Earth. A huge specimen caught in the Southern Ocean, Antarctica, on 20 March 1947 weighed 190 tonnes (418,878 lb) and measured 27.6 m (90 ft 6 in).

Newborn calves are 6-8m (20-26 ft) long and weigh up to 3 tonnes (6,613 lb). The barely visible ovum of the female blue-whale weighing a fraction of a milligram grows to a weight of c. 26 tonnes (57,320 lb) in 22.75 months, made up of 10.75 months' gestation and the first 12 months of life. This is equivalent to an increase of 3x10¹º.
Heaviest A female weighing 190 tonnes (418,877 lb) and measuring 27.6 m (90 ft 6 in) in length was caught in the Southern Ocean on 20 March 1947.
Longest mammal
A female blue whale measuring 33.58 m (110 ft 28 in) landed in 1909 at Grytviken, South Georgia in the South Atlantic.

The longest known animal is the bootlace worm.