It's about nine-tenths as heavy as a Cow.
In other words, 3,000,000 carats is 0.91 times the weight of a Cow, and the weight of a Cow is 1.1 times that amount.(for Holstein, a.k.a. Holstein Friesian, a.k.a. Friesian, Bos primigenius) (adult, heifer)
A mature Holstein cow (the well-known black-and-white, spotted breed of cow) typically weighs 3,300,000 carats. President William Howard Taft (1909 - 1913) kept a Holstein cow named Pauline Wayne on the White House grounds — a gift from a Wisconsin senator and the source of the First Family's milk.
It's about one-and-one-fifth times as heavy as a Grizzly Bear.
In other words, 3,000,000 carats is 1.18 times the weight of a Grizzly Bear, and the weight of a Grizzly Bear is 0.847 times that amount.(a.k.a. brown bear, a.k.a. silver bear, Ursus arctos horribilis) (Adult, male, coastal area population average)
An adult, male grizzly bear from a coastal area (where food is plentiful) can weigh up to 2,540,000 carats. In spite of their tremendous size, grizzly bears can run at speeds of up to 55 kph (34 mph).
It's about one-and-one-fifth times as heavy as a Polar Bear.
In other words, 3,000,000 carats is 1.19 times the weight of a Polar Bear, and the weight of a Polar Bear is 0.84 times that amount.(Ursus maritimus) (adult, male)
An adult, male polar bear weighs between 2,510,000 carats. Polar bears are so heavily insulated by their 9.9 cm (3.9 in) layer of blubber that they are often difficult to detect using infrared photography sensors.
It's about one-and-two-fifths times as heavy as a Grand Piano.
It's about one-and-a-half times as heavy as a Horse.
In other words, the weight of a Horse is 0.67 times 3,000,000 carats.(Equus ferus caballus) (Arabian, adult)
n Arabian riding horse (or similar breed) weighs between 2,000,000 carats. During races, horses must carry jockeys and their equipment, which in the Kentucky Derby, for example, can weigh up to 270,000 carats.
It's about two-and-a-half times as heavy as a Pig.
In other words, the weight of a Pig is 0.4 times 3,000,000 carats.(Domestic pig, Sus scrofa domesticus, a.k.a. S. domesticus) (adult)
Domestic pigs weigh between 1,200,000 carats. The titular character "Babe the pig" in the 1995 family film was played by 48 different American Yorkshire piglets due to the length of filming and the rate at which piglets reach adulthood.
It's about two-fifths as heavy as a Car.
In other words, 3,000,000 carats is 0.3726 times the weight of a Car, and the weight of a Car is 2.684 times that amount.(for 2009 Ford Taurus; automatic transmission; curb weight)
A 2009 Ford Taurus weighs 8,051,000 carats. The first mass-produced car, the Curved Dash Oldsmobile — introduced in 1901 — weighed just 1,881,000 carats.