The copper piece, or cp for short, is an integral part of the default monetary system in the D&D system since its inception. All prices in the core rulebooks and boxed sets are given primarily in gold pieces (gp), with items of lesser value given in silver pieces (sp) or copper pieces, which are monetary fractions of the standard gp.
While the gp is the most common coin used by adventurers, most economies in fantasy settings actually have the silver piece as their foundations, with most wages calculated in silver pieces, not gold. However, as the silver piece is subdivided into copper pieces, the humble cp is by far the most familiar and common coin used in daily transactions throughout most settings.
Size and Weight
The copper piece is generally considered to be a coin, though ingots or trade bars made of copper or other materials may be worth multiple copper pieces or even fractions thereof. In coin form, it is generally described as “approximately the size and weight of a United States half-dollar coin” meaning 30.6mm in diameter and weighing 11.5 grams (approximately 40 to a pound).
In “Basic” D&D (and previous editions) and First Edition AD&D, despite the described weight, copper pieces are considered to weigh a tenth of a pound (1.6 standard ounces) each for encumbrance purposes, with 10 cp weighing one pound. Indeed, in these editions of the game, the basic unit of weight/encumbrance is either the “coin” (cn in Basic D&D) or the “Gold Piece Weight” (gpw), either of which equals one tenth of a pound.
Starting in Second Edition AD&D and continuing through Third and Fourth Editions, copper pieces are considered to weigh approximately a third of a standard ounce (9 grams) each, which equals about fifty gp to a pound, while maintaining the size consistent with previous editions.
As part of the default monetary system of all editions and versions of D&D, the cp is a staple in the system, but its relative value varies depending on edition.
1979 3rd Edition:
- 1 gp = 10 sp = 50 cp = 2 ep = 1/5 pp (meaning 5 gp = 1 Platinum Piece) 
- Note that 1 sp = 5 cp; in all other editions, 1 sp = 10 cp
1981 4th Edition:
First Edition AD&D
- 1 gp = 20 sp = 200 cp = 2 ep = 1/5 pp 
As can be seen, an attempt at replicating a real world economy was made; the 20 sp = 1 gp corresponds to the pre-decimalisation British system of 20 shillings to a Pound Sterling.
Second Edition AD&D
- 1 gp = 10 sp = 100 cp = 2 ep = 1/5 pp 
With 2e, a return to the simple decimal system was made, presumably due to the familiarization of most players with such a system in the modern context.
Third Edition and Beyond
- 1 gp = 10 sp = 100 cp = 2 ep = 1/10 pp
With the introduction of the third edition (and the d20 System), the trend toward decimalization reached its logical conclusion; the platinum piece doubled in value to 10 gp (from the earlier 5 gp), so that with the exception of the electrum piece, each coin is exactly one tenth the value of the coins “above” it, i.e.: 1 pp = 10 gp = 100 sp = 1,000 cp. This continued through the Fourth Edition.
Copper coins in the real world
British Copper coins
The quintessential silver British coin is the pre-decimalisation Penny; a 95% copper (10% tin, technically making it bronze; pure copper is too soft for practical coinage) coin 31mm in diameter weighing 9.4 grams (little over 48 coins to a pound); this matches the D&D cp almost exactly in both size and weight. 12 pennies (abbreviated "d"). The penny was further divided into Half-Pennies - each half the weight of a Penny and about the size of a US quarter dollar. Half-Pennies are further divided into Farthings, again, half the weight of a Half-Penny (a quarter of a Penny) and the size of a modern one cent coin. At one point, Half-Farthing coins were circulated, each half the weight of a Farthing (eight to a Penny), as well as Quarter-Farthings and Third-Farthings, which were minted for the colonies during the Victorian era.
At the other end of the spectrum, King George III (1760-1820) struck a two-penny coin so large and heavy that it was commonly called a "cartwheel penny"; though its face value was two pence, it weighed a whopping 30 grams (pennies weighed more in this era than in later Victorian coinage). The sheer inconvenience of the coin (heavier and larger than the 38.1mm diameter of a US silver dollar, which weighs 26.73 grams [with the later cupro-nickel Eisenhower dollar weighing in at 22.68 grams]) made it not very popular with the masses, and it was removed from circulation as soon as enough silver to make Half-Groat (2d) coins became available.
US Copper coins
Few people today are aware that one cent coins in the US were "Large Cents", between 27mm and 29mm in diameter. These were last minted in 1857, when the US began to strategically reserve copper for the looming conflicts on the horizon and passed the Coinage Act of 1857, which also terminated the production of Half-Cent coins, which were slightly smaller than modern quarter-dollar coins (22mm v. 24.3mm with about the same weight).
From 1864 to 1873, the US minted Two-Cent coins that were about the same size and weight as the pre-1857 half-cent.
Composition remained bronze (95% copper) for most of the "small" (modern) cent's history, until 1982, when it was switched to 97.5% zinc.
Copper coins in different campaign settings
Copper Pieces are called Thumbs in Cormyr, Fandars in Amn, Unarches in Calimport, Nibs in Waterdeep, Thalvers in Cormanthyr and Bits in Southern Lands. Sembia does not use cooper coinage (but they do use copper trade bars), but the cp's place in the economy is taken up by a square iron coin called a Steelpence.
- ↑ Dungeons & Dragons Basic Rules pp B20 4th ed. Jan 1981 - "Moldvay red book"
- ↑ Dungeons & Dragons Basic Rules page 33 3rd ed. Dec 1979 - "Holmes blue book"
- ↑ Dungeons & Dragons Basic Rules pp B47 4th ed. Jan 1981 - "Moldvay B/X red book"
- ↑ Advanced Dungeons & Dragons Player's Handbook pp 35 1st ed. 1978
- ↑ Advanced Dungeons & Dragons Player's Handbook pp __ 2nd ed. 1989
- ↑ SRD
See also: SRD:Wealth and Money