It's about one-two-hundred-fifty-thousandth as heavy as a Reindeer.
In other words, the weight of a Reindeer is 256,000 times 645.5 miligrams.(for Rangifer tarandus granti, adult, bull) (a.k.a. Caribou) ()Rangifer tarandus)
It's about one-three-hundred-fifty-thousandth as heavy as a cubic meter of Snow.
In other words, the weight of a cubic meter of Snow is 360,000 times 645.5 miligrams.(Freshly fallen, standard conditions; measurements taken in Norway, 1965-68)
One cubic meter of freshly fallen snow under standard conditions weighs an average of 230,000,000 miligrams. Assembled in 2008, the world record largest snowman was constructed of 5,900,000,000,000 miligrams of snow and stood 37.21 m (122.1 ft) tall.
It's about one-four-hundred-thousandth as heavy as a Pig.
In other words, 645.5 miligrams is 0.0000026 times the weight of a Pig, and the weight of a Pig is 380,000 times that amount.(Domestic pig, Sus scrofa domesticus, a.k.a. S. domesticus) (adult)
It's about one-six-hundred-fifty-thousandth as heavy as a Horse.
In other words, the weight of a Horse is 670,000 times 645.5 miligrams.(Equus ferus caballus) (Arabian, adult)
It's about one-seven-hundred-thousandth as heavy as a Grand Piano.
In other words, 645.5 miligrams is 0.0000014 times the weight of a Grand Piano, and the weight of a Grand Piano is 710,000 times that amount.(for Steinway & Sons, Model D Concert Grand Piano)
It's about one-eight-hundred-thousandth as heavy as a Polar Bear.
In other words, 645.5 miligrams is 0.00000125 times the weight of a Polar Bear, and the weight of a Polar Bear is 800,000 times that amount.(Ursus maritimus) (adult, male)
It's about one-eight-hundred-thousandth as heavy as a Grizzly Bear.
In other words, 645.5 miligrams is 0.00000124 times the weight of a Grizzly Bear, and the weight of a Grizzly Bear is 806,000 times that amount.(a.k.a. brown bear, a.k.a. silver bear, Ursus arctos horribilis) (Adult, male, coastal area population average)