It's about 0.00000010 times as heavy as a Tyrannosaurus rex.
In other words, 645.5 miligrams is 0.0000001 times the weight of a Tyrannosaurus rex, and the weight of a Tyrannosaurus rex is 10,000,000 times that amount.(for FMNH PR2081, a.k.a. "Sue") (a.k.a. Tyrannosaurus, a.k.a. T-Rex) (estimated live weight)
The notable Tyrannosaurus specimen housed at the Field Museum of Natural History in Chicago, Illinois, "Sue," is estimated to have weighed about 6,400,000,000 miligrams while alive. A renowned predator in popular culture, the teeth of tyrannosaurus rex were up to 33.02 cm (13 in) long.
It's about 0.00000009 times as heavy as an Elephant.
In other words, 645.5 miligrams is 0.00000008591 times the weight of an Elephant, and the weight of an Elephant is 11,640,000 times that amount.(for African bush elephant, Loxodonta africana) (Adult, bull)
A bull African bush elephant weighs between 7,514,000,000 miligrams. Among African elephants, both males and females have tusks (female Asian elephants lack tusks) which can grow to 3 m (10 ft) and weigh up to 90,000,000 miligrams.
It's about 0.00000006 times as heavy as an Anchor of a Cruise Ship.
In other words, 645.5 miligrams is 0.0000000571 times the weight of an Anchor of a Cruise Ship, and the weight of an Anchor of a Cruise Ship is 17,500,000 times that amount.(for QE2 forward anchor, a.k.a. RMS Queen Elizabeth 2)
Each of the forward anchors of the RMS Queen Elizabeth 2 weighs 11,300,000,000 miligrams. The anchor of the QE2 now sits in front of the Holyrood Church in Southampton, England, United Kingdom, along a pedestrian tourist route known as "the QE2 mile."
It's about 0.000000009 times as heavy as The Space Shuttle.
In other words, 645.5 miligrams is 0.0000000091 times the weight of The Space Shuttle, and the weight of The Space Shuttle is 110,000,000 times that amount.(for Endeavour, a.k.a. OV-105, a.k.a. Orbiter Vehicle-105) (empty weight, excluding main engines)
When empty, the space shuttle Endeavour weighs 71,000,000,000 miligrams. The shuttle's spacious cargo bay carried the Chandra X-ray Observatory into orbit in 1999 — a payload that weighed 20,000,000,000 miligrams.
It's about 0.000000006 times as heavy as a Blue Whale.
In other words, 645.5 miligrams is 0.00000000618 times the weight of a Blue Whale, and the weight of a Blue Whale is 162,000,000 times that amount.(Balaenoptera musculus)
Blue whales weigh between 105,000,000,000 miligrams. The largest mammal to have ever lived, blue whales feed almost exclusively on krill — tiny invertebrates weighing about 1,000 miligrams each.
It's about 0.000000004 times as heavy as a House.
In other words, 645.5 miligrams is 0.00000000414 times the weight of a House, and the weight of a House is 242,000,000 times that amount.(149 sq. m, single-level, unfurnished)
A 149 sq. m (1,600 sq. ft), single-story, unfurnished house (without extensive masonry) of the type commonly found in America would weigh approximately 156,000,000,000 miligrams, based on the weight of the included materials. In contrast, a yurt — a type of dwelling structure popular among nomadic peoples of East Asia — typically weighs less than 460,000,000 miligrams.
It's about 0.000000001 times as heavy as Christ the Redeemer (statue).
In other words, 645.5 miligrams is 0.00000000102 times the weight of Christ the Redeemer (statue), and the weight of Christ the Redeemer (statue) is 980,000,000 times that amount.(a.k.a. O Cristo Redentor, a.k.a. Christo redemptor) (Rio de Janeiro, Brazil)
Christ the Redeemer weighs 635,000,000,000 miligrams. The statue overlooks the city of Rio de Janeiro from atop the 709.9-meter (2,329 ft) granite peak in the Tijuca Forest National Park.