It's about one-thirty-thousandth as heavy as The CN Tower
In other words, 0.00000400 megatonnes is 0.0000339240 times the weight of The CN Tower, and the weight of The CN Tower is 29,478 times that amount.(a.k.a. La Tour CN, a.k.a. Canadian National Tower, a.k.a. Canada's National Tower) (Toronto, Canada)
The CN Tower weighs approximately 0.117910 megatonnes. The Tower is home to the world's highest glass floor — a viewing area that allows visitors to look straight down 342 m (1,120 ft) to the ground below.
It's about 30,000 times as heavy as a Battery (D)
In other words, 0.00000400 megatonnes is 29,600 times the weight of a Battery (D), and the weight of a Battery (D) is 0.00003380 times that amount.(Alkaline)
A "D" size battery weighs 0.0000000001350 megatonnes. The D size battery is the oldest of the modern battery sizes, first invented by the National Carbon Company in 1898.
It's about 45,000 times as heavy as a Deck of Cards
In other words, the weight of a Deck of Cards is 0.0000230 times 0.00000400 megatonnes.(ISO 216 B8 size, a.k.a. "poker size" 63 x 88 mm, 52-card deck)
A deck of 52 ISO 216 B8-size playing cards weighs 0.0000000000940 megatonnes. Utilizing nearly 3,700 decks, the record-holding largest card tower was built in early 2010, stood over 3.5 m (11 ft), and weighed over 0.000000230 megatonnes.
It's about one-fifty-thousandth as heavy as The Sears Tower
In other words, 0.00000400 megatonnes is 0.000019820 times the weight of The Sears Tower, and the weight of The Sears Tower is 50,450 times that amount.(officially "Willis Tower" as of 2009) (Chicago, Illinois)
The Willis Tower weighs approximately 0.20180 megatonnes. The outer wall surface of the Tower is covered with black anodized aluminum panels which would total 110,000 sq. m (28 acres) if laid out together.
It's about 60,000 times as heavy as a Battery (C)
In other words, 0.00000400 megatonnes is 62,000 times the weight of a Battery (C), and the weight of a Battery (C) is 0.0000160 times that amount.(Alkaline)
A "C" size battery weighs 0.0000000000650 megatonnes. C batteries are typically used in medium-drain devices such as musical instruments.
It's about 70,000 times as heavy as a Tennis Ball
In other words, 0.00000400 megatonnes is 69,300 times the weight of a Tennis Ball, and the weight of a Tennis Ball is 0.00001440 times that amount.(ITF Standard; for Type 2 ball)
Per International Tennis Federation standard, regulation tennis balls must weigh about 0.00000000005770 megatonnes. Competition balls are also tested for bounce height, with the standards requiring that a ball dropped from 254 cm must bounce back to a height of 135 cm to 147 cm.
It's about one-eighty-five-thousandth as heavy as The Empire State Building