It's about 200 times as heavy as a Sesame Seed.
In other words, 645.5 miligrams is 177 times the weight of a Sesame Seed, and the weight of a Sesame Seed is 0.00565 times that amount.(Sesamum indicum)
A sesame seed weighs approximately 3.64 mg. The McDonald's Big Mac sandwich, which is well-known for its sesame seed top bun, accounts for the consumption of an estimated 2,010,000,000 miligrams of sesame seeds each day.
It's about one-two-hundredth as heavy as a Battery (D).
In other words, 645.5 miligrams is 0.00478 times the weight of a Battery (D), and the weight of a Battery (D) is 209 times that amount.(Alkaline)
A "D" size battery weighs 135,000 miligrams. The D size battery is the oldest of the modern battery sizes, first invented by the National Carbon Company in 1898.
It's about one-two-hundred-fiftieth as heavy as a Baseball.
In other words, 645.5 miligrams is 0.0044427985245764 times the weight of a Baseball, and the weight of a Baseball is 225.08335556255 times that amount.(MLB rules)
Per Major League Baseball rules, a baseball must weigh between 141,747.615625 miligrams and 148,834.99640625 miligrams. A major league pitcher can throw a baseball at up to 150 kph (91 mph) (with a fastball pitch).
It's about one-two-hundred-fiftieth as heavy as a Puck (Hockey).
In other words, 645.5 miligrams is 0.0039598856414703 times the weight of a Puck (Hockey), and the weight of a Puck (Hockey) is 252.5325452653 times that amount.(Ice hockey)
A standard ice hockey puck weighs between 155,922.3771875 miligrams and 170,097.13875 miligrams. Hockey pucks can be shot or passed at speeds of up to 160 kph (99 mph) during games.
It's about one-two-hundred-fiftieth as heavy as a Billiard Ball.
In other words, 645.5 miligrams is 0.0039598856414703 times the weight of a Billiard Ball, and the weight of a Billiard Ball is 252.5325452653 times that amount.(American-style, WPA specifications)
Per the World Pool-Billiard Association, a billiard ball weight must weigh between 155,922.3771875 miligrams and 170,097.13875 miligrams. According to legend, the difficulty in obtaining elephant ivory for the manufacture of billiard balls in the 19th century inspired the search for a replacement material, which led to the development of the first industrial plastic.
It's about one-three-hundred-fiftieth as heavy as a Hamster.
In other words, the weight of a Hamster is 300 times 645.5 miligrams.(for Syrian hamster, a.k.a. golden hamster, a.k.a. Mesocricetus auratus; adult)
An adult Syrian hamster has a typical weight of about 200,000 miligrams. Known for transporting food in the pouches of their cheeks so that they can bury it later, some hamsters can store up to 30,000,000 miligrams of food in their borrows.
It's about one-five-hundredth as heavy as a Human Heart.
In other words, 645.5 miligrams is 0.0021 times the weight of a Human Heart, and the weight of a Human Heart is 480 times that amount.(human; adult)
The average human heart weighs about 310,000 miligrams. Each minute, the heart pumps between 10 and 20 liters (3 to 5 gallons) of blood through its chambers.