It's about as heavy as a Mouse
(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 nine-tenths as heavy as a Battery (AA)
In other words, 0.0000000000210 megatonnes is 0.880 times the weight of a Battery (AA), and the weight of a Battery (AA) is 1.10 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 one-and-two-fifths times as heavy as a Compact disc
It's about three-fifths as heavy as a Light Bulb
In other words, 0.0000000000210 megatonnes is 0.620 times the weight of a Light Bulb, and the weight of a Light Bulb is 1.60 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 one-and-four-fifths times as heavy as a Battery (AAA)
In other words, the weight of a Battery (AAA) is 0.560 times 0.0000000000210 megatonnes.(Alkaline)
An "AAA" size battery weighs 0.0000000000120 megatonnes. Batteries are named by the American National Standards Institute (ANSI) Committee C18 and AAA batteries were given their name because they were smaller than the "AA" and "A" size batteries which were invented first.
It's about half as heavy as a Golf Ball
In other words, 0.0000000000210 megatonnes is 0.45720 times the weight of a Golf Ball, and the weight of a Golf Ball is 2.1870 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 one-third as heavy as a Tennis Ball
In other words, 0.0000000000210 megatonnes is 0.3640 times the weight of a Tennis Ball, and the weight of a Tennis Ball is 2.750 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.