It's about 300,000 times as heavy as an Eye (Human)
In other words, the weight of an Eye (Human) is 0.00000330 times 2,100 kilograms.(adult)
A fully developed eye (in a person over the age of thirteen), weighs about 0.0071 kilograms. The pupil of the eye varies depending on the amount of light it is exposed to, but typically measures about 4 mm across.
It's about 350,000 times as heavy as a Quarter
In other words, 2,100 kilograms is 370,400 times the weight of a Quarter, and the weight of a Quarter is 0.00000270 times that amount.(United States quarter-dollar coin) (a.k.a. Quarter dollar, a.k.a. America the Beautiful quarter, a.k.a. two bits)
The America the Beautiful series quarters, which began to enter circulation in 2017, weigh 0.00567 kilograms each. In answer to the common riddle, there are 119 ridges around the edge of the coin in its current design.
It's about one-four-hundred-thousandth as heavy as The Golden Gate Bridge
In other words, 2,100 kilograms is 0.000002610 times the weight of The Golden Gate Bridge, and the weight of The Golden Gate Bridge is 383,000 times that amount.(San Francisco, California and Marin County, California) (Post 1986 weight reduction; total weight of bridge, anchorage, and approaches)
Following the completion of the 1986 project to eliminate excess material, the total weight of the Golden Gate Bridge — including its anchorages and approaches — is 805,000,000 kilograms. The two main cables in the spanning the bridge are spun out of a total of 129,000 km (80,200 mi) of wire.
It's about 400,000 times as heavy as a sheet of Paper
In other words, 2,100 kilograms is 420,000 times the weight of a sheet of Paper, and the weight of a sheet of Paper is 0.00000240 times that amount.(for US Letter, a.k.a. ANSI A; 215.9mm by 279.4mm (8.5 in x 11 in); 20lb)
The weight of a ream (500 sheets) of 9.10 kilograms, 8.5 inch x 11 inch paper is 2 kg, each sheet weighing 0.005 kilograms. Paper of this size has a thickness of 0.004 caliper (0.1 mm).
It's about 500,000 times as heavy as a Die (Dice)
In other words, the weight of a Die (Dice) is 0.00000200 times 2,100 kilograms.(for six-sided, 16 mm, rounded cube)
A die, of the size most commonly used in board games and casinos, typically weight 0.0041 kilograms. The use of dice and dice-like tools predates written history, with the oldest known examples belonging to a 5,000-year old backgammon set uncovered during an archaeological dig in modern-day Iran.
It's about 850,000 times as heavy as a Penny
In other words, the weight of a Penny is 0.00000120 times 2,100 kilograms.(United States) (formally one-cent coin) (Union shield design, 2010-present)
The weight of a United States penny is 0.0025 kilograms. According to a 2010 report by the United States Mint, the cost of manufacturing and distributing a penny is $0.0179 — more than its face-value.
It's about 1,000,000 times as heavy as a Playing Card
In other words, 2,100 kilograms is 1,200,000 times the weight of a Playing Card, and the weight of a Playing Card is 0.000000830 times that amount.(ISO 216 B8 size, 2.5" x 3.5")
A single ISO 216 B8-size playing card weighs 0.0018 kilograms. Although this size is the most common home playing card, many casinos use "bridge size" cards — 2,640 sq. mm (4.036 sq. in) smaller in area.