It's about fifteen times as heavy as a Grain of Rice
In other words, 315 miligrams is 15 times the weight of a Grain of Rice, and the weight of a Grain of Rice is 0.07 times that amount.(conventional; US; long-, medium-, and short-gran varieties; uncooked)
With great differences in variety, the average among a sampling of common short-, medium- and long-grain rices finds that a single grain weighs about 21 mg before cooking. A staple through most of human history, archaeological evidence indicates that the earliest rice cultivation was about 11,500 years ago.
It's about one-fifteenth as heavy as a sheet of Paper
In other words, 315 miligrams is 0.06 times the weight of a sheet of Paper, and the weight of a sheet of Paper is 16 times that amount.(for US Letter, a.k.a. ANSI A; 215.9mm by 279.4mm (8.5 in x 11 in); 20lb)
The weight of a ream (500 sheets) of 9,100,000 miligrams, 8.5 inch x 11 inch paper is 2,000,000 miligrams, each sheet weighing 5,000 miligrams. Paper of this size has a thickness of 0.004 caliper (0.1 mm).
It's about one-twentieth as heavy as a Quarter
In other words, 315 miligrams is 0.0556 times the weight of a Quarter, and the weight of a Quarter is 18 times that amount.(United States quarter-dollar coin) (a.k.a. Quarter dollar, a.k.a. America the Beautiful quarter, a.k.a. two bits)
The America the Beautiful series quarters, which began to enter circulation in 2017, weigh 5,670 miligrams each. In answer to the common riddle, there are 119 ridges around the edge of the coin in its current design.
It's about one-twenty-fifth as heavy as an Eye (Human)
In other words, 315 miligrams is 0.04 times the weight of an Eye (Human), and the weight of an Eye (Human) is 23 times that amount.(adult)
A fully developed eye (in a person over the age of thirteen), weighs about 7,100 miligrams. The pupil of the eye varies depending on the amount of light it is exposed to, but typically measures about 4 mm across.
It's about one-fortieth as heavy as a Battery (AAA)
In other words, 315 miligrams is 0.03 times the weight of a Battery (AAA), and the weight of a Battery (AAA) is 38 times that amount.(Alkaline)
An "AAA" size battery weighs 12,000 miligrams. Batteries are named by the American National Standards Institute (ANSI) Committee C18 and AAA batteries were given their name because they were smaller than the "AA" and "A" size batteries which were invented first.
It's about one-fiftieth as heavy as a Compact disc
In other words, 315 miligrams is 0.02 times the weight of a Compact disc, and the weight of a Compact disc is 48 times that amount.(a.k.a. CD)
A compact disc typically weighs 15,000 miligrams. Data is stored on CDs by encoding into the track a series of tiny pits — each between 3.5 and 850 µm (0.00014 and 0.033 in) in length.
It's about one-sixty-fifth as heavy as a Mouse
In other words, 315 miligrams is 0.02 times the weight of a Mouse, and the weight of a Mouse is 67 times that amount.(a.k.a. "House mouse", Mus musculus) (adult)
The weight of a mouse is typically an average of 21,000 miligrams. While most mice typically live two to three years, the Methuselah Mouse Prize — an award administered by a non-profit organization which advances aging-related research — was once awarded to a team of scientists whose research resulted in a mouse living just under five years.