It's about as heavy as a Grizzly Bear.
(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 521 kg. 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-tenth times as heavy as a Polar Bear.
In other words, 521 kilograms is 1.01 times the weight of a Polar Bear, and the weight of a Polar Bear is 0.99 times that amount.(Ursus maritimus) (adult, male)
It's about nine-tenths as heavy as The Heart of a Blue Whale.
It's about one-and-one-fifth times as heavy as a Grand Piano.
In other words, the weight of a Grand Piano is 0.83 times 521 kilograms.(for Steinway & Sons, Model D Concert Grand Piano)
It's about one-and-one-fifth times as heavy as a Horse.
In other words, the weight of a Horse is 0.83 times 521 kilograms.(Equus ferus caballus) (Arabian, adult)
It's about three-fourths as heavy as a Cow.
In other words, the weight of a Cow is 1.3 times 521 kilograms.(for Holstein, a.k.a. Holstein Friesian, a.k.a. Friesian, Bos primigenius) (adult, heifer)
It's about two times as heavy as a Pig.
In other words, 521 kilograms is 2.1 times the weight of a Pig, and the weight of a Pig is 0.48 times that amount.(Domestic pig, Sus scrofa domesticus, a.k.a. S. domesticus) (adult)