It's about 20,000 times as heavy as a Golf Ball
In other words, 999 kilograms is 21,750 times the weight of a Golf Ball, and the weight of a Golf Ball is 0.000045980 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 0.04593 kilograms. 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 15,000 times as heavy as a Tennis Ball
In other words, 999 kilograms is 17,300 times the weight of a Tennis Ball, and the weight of a Tennis Ball is 0.00005780 times that amount.(ITF Standard; for Type 2 ball)
Per International Tennis Federation standard, regulation tennis balls must weigh about 0.0577 kilograms. 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 15,000 times as heavy as a Battery (C)
In other words, the weight of a Battery (C) is 0.0000670 times 999 kilograms.(Alkaline)
A "C" size battery weighs 0.065 kilograms. C batteries are typically used in medium-drain devices such as musical instruments.
It's about 10,000 times as heavy as a Deck of Cards
In other words, 999 kilograms is 11,000 times the weight of a Deck of Cards, and the weight of a Deck of Cards is 0.0000910 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 0.094 kilograms. 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 272 kg.
It's about 7,500 times as heavy as a Battery (D)
In other words, the weight of a Battery (D) is 0.000135 times 999 kilograms.(Alkaline)
A "D" size battery weighs 0.1350 kilograms. The D size battery is the oldest of the modern battery sizes, first invented by the National Carbon Company in 1898.
It's about 7,000 times as heavy as a Baseball
In other words, 999 kilograms is 6,875.84155856210 times the weight of a Baseball, and the weight of a Baseball is 0.00014543674275838 times that amount.(MLB rules)
Per Major League Baseball rules, a baseball must weigh between 0.1417476156250 kilograms and 0.148834996406250 kilograms. 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 6,000 times as heavy as a Billiard Ball
In other words, 999 kilograms is 6,128.46747610970 times the weight of a Billiard Ball, and the weight of a Billiard Ball is 0.00016317293089965 times that amount.(American-style, WPA specifications)
Per the World Pool-Billiard Association, a billiard ball weight must weigh between 0.15592237718750 kilograms and 0.170097138750 kilograms. According to legend, the difficulty in obtaining elephant ivory for the manufacture of billiard balls in the 19th century inspired the search for a replacement material, which led to the development of the first industrial plastic.