It's about as heavy as a Rhinoceros
(for Black rhinoceros, Diceros bicornis) (Adult, male)
An adult black rhinoceros weighs between 0.00000210 megatonnes. Rhinoceros are extremely aggressive — nearly one of every two males will die as a result of fighting with other rhinoceros.
It's about one-and-one-tenth times as heavy as a Giraffe
In other words, 0.00000210 megatonnes is 1.09 times the weight of a Giraffe, and the weight of a Giraffe is 0.9170 times that amount.(Giraffa camelopardalis reticulata) (adult, male, maximum of range)
An adult, male giraffe can weigh up to 0.000001930 megatonnes. Reaching 5.5 m (18 ft) in height by adulthood, giraffe calves can grow as much as 3 cm (1 in) per day.
It's about one-and-one-fourth times as heavy as a Car
In other words, 0.00000210 megatonnes is 1.2710 times the weight of a Car, and the weight of a Car is 0.78680 times that amount.(for 2009 Ford Taurus) (curb weight)
A 2009 Ford Taurus weighs 0.0000016520 megatonnes. The first mass-produced car, the Curved Dash Oldsmobile — introduced in 1901 — weighed just 0.0000003860 megatonnes.
It's about four-fifths as heavy as The Tongue of a Blue Whale
In other words, 0.00000210 megatonnes is 0.780 times the weight of The Tongue of a Blue Whale, and the weight of The Tongue of a Blue Whale is 1.30 times that amount.(Balaenoptera musculus) (adult)
The tongue of a Blue Whale can weigh up to 0.00000270 megatonnes. Despite their tremendous size, blue whales feed almost exclusively on tiny crustaceans called krill and cannot swallow anything much larger than a beach ball.
It's about three-fifths as heavy as a Hippopotamus
In other words, 0.00000210 megatonnes is 0.560 times the weight of a Hippopotamus, and the weight of a Hippopotamus is 1.790 times that amount.(Hippopotamus amphibius) (adult, male)
The average weight of an adult male hippopotamus ranges from 0.000003750 megatonnes. Appearances to the contrary, adult hippos cannot swim or float in water; they actually move by leaping and walking across lake bottoms at about 8 kph (5 mph).
It's about one-third as heavy as an Elephant
In other words, the weight of an Elephant is 2.90 times 0.00000210 megatonnes.(for African bush elephant, Loxodonta africana) (Adult, bull)
A bull African bush elephant weighs about 0.00000610 megatonnes. Among African elephants, both males and females have tusks (whereas female Asian elephants, Elephas maximus, do not have tusks) which can grow to 3 m (10 ft) and typically weigh about 0.00000400 megatonnes
It's about one-third as heavy as a Tyrannosaurus rex
In other words, the weight of a Tyrannosaurus rex is 3 times 0.00000210 megatonnes.(for FMNH PR2081, a.k.a. "Sue") (a.k.a. Tyrannosaurus, a.k.a. T-Rex) (estimated live weight)
The notable Tyrannosaurus specimen housed at the Field Museum of Natural History in Chicago, Illinois, "Sue," is estimated to have weighed about 0.00000640 megatonnes while alive. A renowned predator in popular culture, the teeth of tyrannosaurus rex were up to 33.02 cm (13 in) long.