It's about 7,500 times as heavy as a Tennis Ball
In other words, 0.000000420 megatonnes is 7,280 times the weight of a Tennis Ball, and the weight of a Tennis Ball is 0.000137 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 9,000 times as heavy as a Golf Ball
In other words, 0.000000420 megatonnes is 9,144 times the weight of a Golf Ball, and the weight of a Golf Ball is 0.0001094 times that amount.(per R&A USGA Rules of Golf; maximum rule weight)
According to the Rules of Golf (as approved by the United States Golf Association and the Rules Committee of the Royal and Ancient Golf Club of Saint Andrews), golf balls must weigh no more than 0.000000000045930 megatonnes. Golf balls are not required to have the familiar dimpled pattern, but the design has been popular since its invention in 1905 because it reduces drag while increasing lift.
It's about 10,000 times as heavy as a Light Bulb
In other words, 0.000000420 megatonnes is 12,000 times the weight of a Light Bulb, and the weight of a Light Bulb is 0.0000830 times that amount.(a.k.a. lamp) (for A19-size, 60w, incandescent bulb by Bulbrite; package weight)
A standard, sixty-watt light bulb weighs about 0.0000000000340 megatonnes. The tightly-coiled filament inside a bulb of this size would measure about 579mm if uncoiled and stretched out.
It's about 20,000 times as heavy as a Battery (AA)
In other words, 0.000000420 megatonnes is 18,000 times the weight of a Battery (AA), and the weight of a Battery (AA) is 0.0000560 times that amount.(Alkaline)
An "AA" size battery weighs 0.0000000000240 megatonnes. AA batteries came into common use during World War II and were given their name by the American National Standards Institute (ANSI) Committee C18 because they were smaller than the "A" size batteries which were invented first.
It's about 20,000 times as heavy as a Mouse
In other words, the weight of a Mouse is 0.0000500 times 0.000000420 megatonnes.(a.k.a. "House mouse", Mus musculus) (adult)
The weight of a mouse is typically an average of 0.0000000000210 megatonnes. While most mice typically live two to three years, the Methuselah Mouse Prize — an award administered by a non-profit organization which advances aging-related research — was once awarded to a team of scientists whose research resulted in a mouse living just under five years.
It's about one-twenty-five-thousandth as heavy as The Eiffel Tower
It's about 30,000 times as heavy as a Compact disc
In other words, 0.000000420 megatonnes is 28,000 times the weight of a Compact disc, and the weight of a Compact disc is 0.0000360 times that amount.(a.k.a. CD)
A compact disc typically weighs 0.0000000000150 megatonnes. Data is stored on CDs by encoding into the track a series of tiny pits — each between 3.5 and 850 µm (0.00014 and 0.033 in) in length.