It's about half as heavy as a Basketball
In other words, 0.000000000310 megatonnes is 0.497042191110 times the weight of a Basketball, and the weight of a Basketball is 2.0119016411 times that amount.(NBA official ball standards, Size 7)
A regulation NBA basketball, manufactured by Spalding, is known as a Size 7 ball and weighs 0.000000000623689508750 megatonnes. These balls have 4,118 pebbles each with a diameter of 2.5 mm
It's about two times as heavy as a Baseball
In other words, 0.000000000310 megatonnes is 2.13364452768190 times the weight of a Baseball, and the weight of a Baseball is 0.468681632308480 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).
It's about two-and-a-half times as heavy as a Battery (D)
In other words, the weight of a Battery (D) is 0.4350 times 0.000000000310 megatonnes.(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 three-tenths as heavy as a liter of Water
In other words, 0.000000000310 megatonnes is 0.30999130 times the weight of a liter of Water, and the weight of a liter of Water is 3.2258970 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).
It's about three-and-a-half times as heavy as a Deck of Cards
In other words, the weight of a Deck of Cards is 0.30 times 0.000000000310 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-fourth as heavy as a Human Brain
In other words, 0.000000000310 megatonnes is 0.230 times the weight of a Human Brain, and the weight of a Human Brain is 4.350 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 five times as heavy as a Battery (C)
In other words, 0.000000000310 megatonnes is 4.80 times the weight of a Battery (C), and the weight of a Battery (C) is 0.210 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.