The gold piece, or gp for short, is the foundation 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 gp, with items of lesser value given in silver pieces (sp) or copper pieces (cp), which are monetary fractions of the standard gp.
Size and Weight
The gold piece is generally considered to be a coin, though ingots or trade bars made of gold or other materials may be worth multiple gold pieces. 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, gold pieces are considered to weigh a tenth of a pound (1.6 standard ounces) each for encumbrance purposes, with 10 gp 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, gold pieces are considered to weigh approximately a third of a standard ounce (9 grams) each, which equal about fifty gp to a pound, while maintaining the size equal.
As part of the default monetary system of all editions and versions of D&D, the gp is a staple of the system, but its relative value varies depending on edition.
1979 3rd Edition:
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.
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.
3e offers a table that indicates that 1 gp can buy a goat or a pound of cinnamon. Magical Items can range in value from the low 12 gp, 5 sp (sometimes described as 12.5 gp) single-use 0-level scroll to artifacts valued at hundreds of thousands (or even over a million) gold pieces.
Gold coins in the real world
Roman gold coins
Gold was used for coinage very infrequently until the time of Julius Caesar, who introduced a standardised coin called aureus, which was struck regularly. It weighed 8 gramm, 1/40 of a Roman pound, but later its weight decreased to 1/45 of a pound in the time of Nero and to 1/50 of a pound in the time of Caracalla. The aureus had a fixed value of 25 denarii (Roman silver coin). Emperor Constantine I introduced the solidus to replace the aureus. Solidi were wider and thinner than the aureus, with the exception of some dumpy issues from the Byzantine Empire. The weight and fineness of the solidus remained relatively constant throughout its long production, with few exceptions. Fractions of the solidus known as semissis (half-solidi) and tremissis (one-third solidi) were also produced.
British gold coins
The noble was the first English gold coin produced in quantity, having been preceded by the twenty pence coin and the florin (also called double leopard) earlier in the reigns of King Henry III and King Edward III, which saw little circulation. The coin was introduced during the second coinage (1344-1346) of King Edward III, when the coin weighed 138.5 grains (9.0 grams); during the kings' third coinage (1346-1351) the weight of the coin was reduced to 128.5 grains (8.3 grams), while in his fourth coinage (1351-1377) it became even lighter, at 120 grains (7.8 grams).
A gold sovereign is a gold coin first issued in 1489 for Henry VII of England and still in production as of 2006 (equal to a pound sterling). Those original sovereigns were 23 carat (96%) gold and weighed 240 grains or one-half of a troy ounce (15.6 grams). Henry VIII reduced the purity to 22 carats (92%), which eventually became the standard; the weight of the sovereign was repeatedly lowered until when it was revived after the Great Recoinage law of 1816, the gold content was fixed at the present 113 grains (7.32 g), equivalent to 0.2354 Troy ounces. Sovereigns were discontinued after 1604, being replaced by unites, and later by laurels. Production of sovereigns restarted in 1817.
The guinea coin of 1663 was the first British machine-struck gold coin. The coin was originally worth one pound, which was twenty shillings; but rises in the price of gold caused the value of the guinea to increase, at times as high as thirty shillings. 44½ guineas would be made from one Troy pound of 11/12 finest gold, each weighing 129.4 grains. In 1670 the weight of the coin was reduced from 8.4–8.5 g to 8.3–8.4 g, but the price of gold continued to increase, and by the 1680s the coin was worth 22 shillings. The diameter of the coin was 25 millimetres throughout Charles II's reign, and the average gold content (from an assay done in 1773) was 0.9100.
Gold coins in different campaign settings
Gold Pieces are called Golden Lions in Cormyr, Dantars in Amn, Bicentas in Calimport, Dragons in Waterdeep, Shilmaers in Cormanthyr and Dinars in Southern Lands. Sembia mints five-sided coins of the same weight called Golden Lions (not to be confused with the eponymous Cormyrean gold pieces.
The Dragonlance Campaign Setting greatly devalues the intrinsic worth of the gold piece and replaces it with the Steel Piece (Stl) as the default value in the rulebooks, with 1 Stl = 1 standard gp. In the Setting itself, the actual value of a gp relative to the other coin types depends on the region; in some areas (Seeker Lands) the gp is literally worthless, while in others it may be worth between 1/10th Stl, 1/40th Stl or 1/50th Stl.
- ↑ Dungeons & Dragons Basic Rules pp B20 4th ed. Jan 1981 - "Moldvay red book"
- ↑ Dungeons & Dragons Basic Rules page 34 3rd ed. Dec 1979 - "Holmes blue book"
- ↑ Dungeons & Dragons Basic Rules pp B47 4th ed. Jan 1981 - "Moldvay red book"
- ↑ Advanced Dungeons & Dragons Player's Handbook pp 35 1st ed. 1978
- ↑ Advanced Dungeons & Dragons Player's Handbook pp __ 2nd ed. 1989
- ↑ SRD
- ↑ Dragonlance Adventures Hardcover, 1987