It's about as heavy as a Battery (C)
A "C" size battery weighs 0.0000000000650 megatonnes. C batteries are typically used in medium-drain devices such as musical instruments.
It's about one-and-one-tenth times as heavy as a Tennis Ball
In other words, 0.0000000000650 megatonnes is 1.130 times the weight of a Tennis Ball, and the weight of a Tennis Ball is 0.8850 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-and-two-fifths times as heavy as a Golf Ball
In other words, 0.0000000000650 megatonnes is 1.4150 times the weight of a Golf Ball, and the weight of a Golf Ball is 0.70670 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 seven-tenths as heavy as a Deck of Cards
In other words, 0.0000000000650 megatonnes is 0.690 times the weight of a Deck of Cards, and the weight of a Deck of Cards is 1.40 times that amount.(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-and-nine-tenths times as heavy as a Light Bulb
In other words, the weight of a Light Bulb is 0.530 times 0.0000000000650 megatonnes.(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 half as heavy as a Battery (D)
In other words, 0.0000000000650 megatonnes is 0.4810 times the weight of a Battery (D), and the weight of a Battery (D) is 2.08 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 two-fifths as heavy as a Baseball
In other words, 0.0000000000650 megatonnes is 0.447377078384920 times the weight of a Baseball, and the weight of a Baseball is 2.23525086177890 times that amount.(MLB rules)
Per Major League Baseball rules, a baseball must weigh between 0.0000000001417476156250 megatonnes and 0.000000000148834996406250 megatonnes. A major league pitcher can throw a baseball at up to 150 kph (91 mph) (with a fastball pitch), with record-setting pitches as fast as 171 kph (106 mph).