It's about 150 times as heavy as a Brick
In other words, the weight of a Brick is 0.0071 times 0.000000420 megatonnes.(Standard, traditional face brick - 1,900 cu. cm (120 cu. in))
A standard, traditional face brick weighs an average of 0.00000000290 megatonnes. The steeple of the Church of St. Martin in Landshut, Germany is said to be the tallest brick tower in the world at a height of 130.6 m (428.5 ft) and was constructed using an estimated 650,000 bricks.
It's about one-one-hundred-fiftieth as heavy as The Space Shuttle
In other words, the weight of The Space Shuttle is 170 times 0.000000420 megatonnes.(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 0.0000710 megatonnes. The shuttle's spacious cargo bay carried the Chandra X-ray Observatory into orbit in 1999 — a payload that weighed 0.0000200 megatonnes.
It's about 200 times as heavy as a Chihuahua
In other words, 0.000000420 megatonnes is 187 times the weight of a Chihuahua, and the weight of a Chihuahua is 0.00535 times that amount.(a.k.a. Chihuahue(o) (FCI standard)
The F&d&ration Cynologique Internationale (FCI) calls for Chihuahuas to weigh about 0.000000002250 megatonnes. Relative to their body sizes, Chihuahuas have the largest brain size of any dog breed.
It's about one-two-hundred-fiftieth as heavy as a Blue Whale
In other words, 0.000000420 megatonnes is 0.00402 times the weight of a Blue Whale, and the weight of a Blue Whale is 249 times that amount.(Balaenoptera musculus)
Blue whales weigh between 0.000105 megatonnes. The largest mammal to have ever lived, blue whales feed almost exclusively on krill — tiny invertebrates weighing about 0.000000000001000 megatonnes each.
It's about 300 times as heavy as a Human Brain
In other words, 0.000000420 megatonnes is 311 times the weight of a Human Brain, and the weight of a Human Brain is 0.00322 times that amount.(adult)
The average weight of an adult human brain is between 0.000000001350 megatonnes. In humans and primates, sight and vision utilize about 30 different parts of the brain which together account for about half of the brain's size.
It's about one-three-hundred-fiftieth as heavy as a House
In other words, 0.000000420 megatonnes is 0.00269 times the weight of a House, and the weight of a House is 372 times that amount.(149 sq. m, single-level, unfurnished)
A 149 sq. m (1,600 sq. ft), single-story, unfurnished house (without extensive masonry) of the type commonly found in America would weigh approximately 0.000156 megatonnes, based on the weight of the included materials. In contrast, a yurt — a type of dwelling structure popular among nomadic peoples of East Asia — typically weighs less than 0.000000460 megatonnes.
It's about 400 times as heavy as a liter of Water
In other words, 0.000000420 megatonnes is 419.98820 times the weight of a liter of Water, and the weight of a liter of Water is 0.002381019 times that amount.(fresh; 4° C / 39.2° F; maximum density)
Contrary to popular belief, 1 liter (0.0.264172052358148 gal) of water at 4° C / 39.2° F (its point of maximum density) weighs 0.0000000010000280 megatonnes rather than 1 kg exactly. The total volume of water on the planet Earth is about 13,590,000,000,000,000,000 (13.59 quntillion) L (3,590,000,000,000,000,000 gallons).