| Reference | Grams (g) | Drams (dr) |
|---|---|---|
| A sheet of A4 paper (80 gsm) | 5 g | 2.82192 dr |
| One litre of water | 1000 g | 564.383 dr |
| Average adult human | 70000 g | 39506.8 dr |
| A small car | 1400000 g | 790137 dr |
The gram is a unit of mass equal to one thousandth of a kilogram. Its symbol is g. Although the kilogram is the SI base unit, the gram is the one that carries the prefixes, so milligram and microgram are built on the gram rather than on the kilogram.
That awkwardness is historical. The original metric system of 1795 defined the gramme as the mass of one cubic centimetre of water at the temperature of melting ice. It was intended as the base unit, but a one-gram standard is too light to be a practical reference: a speck of dust or a fingerprint changes it measurably. The thousandfold-larger kilogram was made the standard artefact instead, and the SI inherited the arrangement, leaving the base unit as the only one carrying a prefix in its own name.
Cooking outside the English-speaking world runs on grams, and increasingly inside it as well. Weighing flour rather than measuring it by volume removes the largest source of error in baking, because a cup of flour can vary by twenty per cent depending on how it was packed. Professional bakers work entirely in grams and express recipes as percentages of flour weight.
Nutrition panels report protein, fat, carbohydrate, sugar and fibre in grams, so the unit is the everyday currency of dietary arithmetic. Postal services price letters and small parcels in grams, and precious metals, though traded in troy ounces, are sold to the public in gram bars.
It is also the unit the SI prefixes attach to, which is why the system has a base unit that already carries a prefix. Smaller and larger masses are named from the gram and never from the kilogram: a thousandth of a gram is a milligram, not a microkilogram, and a million grams is a megagram, better known as the tonne. The rule spares the language a set of double prefixes that would otherwise be unavoidable, but it leaves the kilogram in the odd position of being the only base unit whose name contains one. Postal tariffs show the gram at work in ordinary life: letter rates step at 20, 50 and 100 grams, and a sheet of office paper weighs about five.
One gram equals 0.001 kilograms, one thousand milligrams, or about 0.035 ounces.
The dram is a unit of mass equal to one sixteenth of an avoirdupois ounce, or about 1.7718 grams. Its symbol is dr. There are 256 drams in a pound and 27.34375 grains in a dram, a set of numbers that shows how far the avoirdupois system drifted from tidy arithmetic.
The name descends from the Greek drachma through Latin and Old French, and the same root gives the modern currency of Armenia and the historical coin of Athens. The apothecaries' dram was a different and larger unit, one eighth of a troy ounce or 3.888 grams, and pharmacists used it until the twentieth century. Recipes and old medical texts therefore need reading with care, since an unqualified dram may be either.
Modern survival is narrow but real. Shotgun shells are the best-known case: the dram equivalent printed on a box of cartridges is a legacy figure describing the propellant charge in terms of the black powder that would have produced the same velocity, not the actual weight of modern smokeless powder. American recipes occasionally call for drams, and the unit persists in some descriptions of small hardware and fishing weights.
For everyday purposes the dram is now a curiosity, kept alive by its appearance on packaging and in older texts rather than by any working need. Where precision matters the same quantity is stated in grams, and where tradition matters the word survives without its arithmetic being examined too closely.
Two other drams complicate the picture. The apothecaries' dram, used in pharmacy until the twentieth century, was one eighth of a troy ounce and weighed about 3.888 grams, more than twice the avoirdupois dram described here. The fluid dram is a measure of volume rather than mass, one eighth of a fluid ounce, and it still appears on the graduations of old medicine glasses and on some American pharmacy equipment. A recipe or a formula written before the metric era therefore has to be read with its system identified first, because the same word can mean two different masses and a volume, and nothing in the notation distinguishes them.
One dram equals about 1.7718 grams, one sixteenth of an ounce, or 27.34375 grains.