It's about one-and-three-fourths times as heavy as an Anchor of a Cruise Ship
In other words, 20 tonnes is 1.77 times the weight of an Anchor of a Cruise Ship, and the weight of an Anchor of a Cruise Ship is 0.565 times that amount.(for QE2 forward anchor, a.k.a. RMS Queen Elizabeth 2)
Each of the forward anchors of the RMS Queen Elizabeth 2 weighs 11.30 tonnes. The anchor of the QE2 now sits in front of the Holyrood Church in Southampton, England, United Kingdom, along a pedestrian tourist route known as "the QE2 mile."
It's about three times as heavy as a Tyrannosaurus rex
In other words, 20 tonnes is 3.1 times the weight of a Tyrannosaurus rex, and the weight of a Tyrannosaurus rex is 0.32 times that amount.(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 6.4 tonnes while alive. A renowned predator in popular culture, the teeth of tyrannosaurus rex were up to 33.02 cm (13 in) long.
It's about three-and-a-half times as heavy as an Elephant
In other words, 20 tonnes is 3.3 times the weight of an Elephant, and the weight of an Elephant is 0.3 times that amount.(for African bush elephant, Loxodonta africana) (Adult, bull)
A bull African bush elephant weighs about 6.10 tonnes. 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 4 tonnes
It's about three-tenths as heavy as The Space Shuttle
In other words, 20 tonnes is 0.28 times the weight of The Space Shuttle, and the weight of The Space Shuttle is 3.6 times that amount.(for Endeavour, a.k.a. OV-105, a.k.a. Orbiter Vehicle-105) (empty weight, excluding main engines)
When empty, the space shuttle Endeavour weighs 71 tonnes. The shuttle's spacious cargo bay carried the Chandra X-ray Observatory into orbit in 1999 — a payload that weighed 20 tonnes.
It's about one-fifth as heavy as a Blue Whale
In other words, 20 tonnes is 0.191 times the weight of a Blue Whale, and the weight of a Blue Whale is 5.24 times that amount.(Balaenoptera musculus)
Blue whales weigh between 105 tonnes. The largest mammal to have ever lived, blue whales feed almost exclusively on krill — tiny invertebrates weighing about 0.000001000 tonnes each.
It's about five-and-a-half times as heavy as a Hippopotamus
In other words, 20 tonnes is 5.3 times the weight of a Hippopotamus, and the weight of a Hippopotamus is 0.19 times that amount.(Hippopotamus amphibius) (adult, male)
The average weight of an adult male hippopotamus ranges from 3.80 tonnes. 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-tenth as heavy as The Statue of Liberty (without base)
In other words, 20 tonnes is 0.14 times the weight of The Statue of Liberty (without base), and the weight of The Statue of Liberty (without base) is 7.1 times that amount.(a.k.a. Liberty Enlightening the World, a.k.a. La Liberté éclairant le monde) (total weight, including foundation)
The total weight of the Statue of Liberty — the Statue's copper and framework only, excluding the base — is roughly 140 tonnes. The statue was designed using an optical trick known as "forced perspective" to make the statue appear proportionally correct when viewed from its base and is, in actuality, disproportionately large at the top.