Gold-Silver-Copper Standard

A popular convention for fictional works stuck in Medieval Stasis or otherwise "primitive" settings is to have money handled by the exchange of precious metals. In almost all of these cases, there will be different denominations of coins differentiated entirely by what metal they're made out of. Usually this takes the form of the Olympic metals—gold as the highest, silver second, and bronze last (though in coinage, copper is used instead of bronze more often than not). Sometimes more valuable metals are added above gold—commonly platinum.

There is some Truth in Television to this. Gold and silver coins were used for much of history, and even modern day currencies often invoke this by making their highest denomination coins golden, their middle ones silvery, and their lowest ones copper or bronze. Obviously, gold is more valuable than silver, which is itself more valuable than copper or bronze, but the value of individual coins depends as much on the weight and purity of the coin as it does on the value of the metal itself—this is rarely reflected in fiction. Also rarely used is multiple denominations of coin made out of the same metal; a gold coin weighing twice as much as another gold coin would be worth twice the amount, but don't expect to see anything besides a generic "gold piece" ever mentioned.

When using the Gold-Silver-Copper Standard, expect the coins to use a decimal system—a coin will be worth ten times the denomination below it and one tenth the denomination above it, so that 1 gold = 10 silver = 100 copper (though occasionally units of 100 are used instead of 10). This has absolutely no basis in fact—even if coins were minted to deliberately have this relationship, the prices of metals varies, and the "exchange rate" between different coins would fluctuate with time just as exchange rates between currencies do. This is generally an Acceptable Break From Reality, as very few people would be interested in doing "realistic" calculations of this nature, especially writers.

The trope title is a reference to the gold standard, when paper money is set to be worth a fixed amount of gold, but the trope is otherwise unrelated to the concept. Expect to see the coins in a Gold-Silver-Copper Standard economy referred to as [metal] piece or [metal] coin; when they're given another name, it can overlap with Fictional Currency. Tasty Gold is related, for checking the purity of the gold coins. Often a Global Currency, though that's understandable, as the value in the coins comes from the precious metal itself. May be combined with Silver Has Mystic Powers to make gold more (and bronze/copper less) powerful than silver. For settings where transactions are done almost exclusively in gold, see Cheap Gold Coins.

Examples of Gold-Silver-Copper Standard include:

Anime and Manga

Spice and Wolf has... far too many currency systems to even remember, but their values are definitely based on gold and silver content. More important than that, however, is the trust that the traders give to the coin. A tiny shift in precious metal content can lead to huge shift in value; very much like it used to be in real life, in fact.

Literature

Harry Potter uses gold, silver, and bronze coins as money in the wizarding world; they're called galleons, sickles, and knuts, respectively. Their relative values are not decimalized, but rather have 17 sickles to the galleon and 29 knuts to the sickle, presumably to make their system similar to the pre-decimalized British currency (or perhaps as another way of making the wizarding world whimsical/whacky).
- Deconstructed in the fanfic Harry Potter and the Methods of Rationality, where Harry quickly realizes that since the wizarding world fixes the exchange rate of precious metals in a different way that the Muggle world, he could quickly become rich by buying and selling cyclically between the two worlds.
- Thinking In Little Green Boxes also deconstructs this, with Harry withdrawing a large chunk of his wizard account to buy "useful" real world things.
- In other fics (written, presumably, by more economically-savvy writers), the goblins have instituted policies (or enchantments upon their coinage) to prevent this kind of arbitrage across the worlds. In some cases, this includes actually debasing the metal of the galleon so that it contains only a fraction of the gold that it appears to be -- or rendering the coins a fiat currency by manufacturing them out of "stabilized leprechaun gold".
Gor has gold and silver Tarns, and silver and copper Tarsks. A still smaller unit of exchange is the "Tarsk-Bit". Gold double-tarns are mentioned at least once - in Assassin of Gor, the hero offers to up the stakes in a street Kaissa game to a tarn of gold and of double weight if the blind chessmaster, who is losing deliberately, can find a win; and this represents more than a year's winnings for a Player.
Dragonlance plays it straight at first, but subverts the standard after the Cataclysm by having iron become the coin of choice.
The currency in Tamora Pierce's Tortall novels is based on gold, silver, and copper pieces.
A Song of Ice and Fire uses golden dragons, silver stags and copper stars, the first two named after the Animal Motifs used by the previous and current dynasty, respectively.
The Saga of Recluce uses this straight, including the decimal values, and even naming them simply "golds", "silvers" and "coppers".
The Wheel of Time uses this system throughout the continent on which the books are set. There are three denominations for each material, pennies, marks and crowns, which differ by size. Though the decimal conversion system is followed in some regions, it's not universal, as different countries have different weights of coin, and, of course, a gold mark is worth a lot more than a silver crown.
Midkemian currency has the denominations sovereign, royal and common. The only difference between the coins is the metal used to make them (sovereigns are gold, royals silver and commons copper). Gems of various types exist as an unofficial currency, and are used alongside coins for making large purchases.
The Knight and Rogue Series has gold, silver, and brass, with names like roundels and fracts. The Farsala Trilogy, another series by Hilari Bell, uses the same metals, but gives them different names.
Applies to the Garrett P.I. series, although the usual 10-to-1 exchange rate is subverted because events in the ongoing Cantard war keep changing the value of silver.

Tabletop Games

Dungeons & Dragons is the Trope Codifier in modern media; coins from most valuable to least are platinum, gold, silver, and copper at a ratio of 10:1. Previous editions had outliers (electrum, a gold/silver alloy, at half a gold each) and at least one non-decimal exchange rate (5 gold to 1 platinum, 20 silver to 1 gold in 1st Edition, 5 copper to 1 silver in pre-1st-Edition Basic D&D), but these have been done away with over the years.
- In 1st Edition AD&D, the gold piece was more than the basic unit of currency. It was also the basic unit of weight. All coins, including gold pieces, weighed 1/10 of a pound each, and all weights—the weight of a suit of armor, the carrying capacity of a character with 17 Strength, the strength of a telekinesis spell, etc. -- were given in units of gold pieces. (2nd Edition reduced the weight of coins to 1/50 of a pound each, and listed weights and weight-limits in plain old pounds.)
Similarly RuneQuest, but prices are usually given in silver Lunars, with copper Clacks being the common street currency and gold Wheels usually having to be changed for silver before they can be spent (though Sun-worshipers use gold on principle).
Role Master has a long line of metal coinage, all with decimal exchange rates. 10 iron pieces are worth 1 tin piece, 10 tin pieces = 1 copper piece, 10 copper pieces = 1 bronze piece, 10 bronze pieces = 1 silver piece, 10 silver pieces = 1 gold piece, and 1000 gold pieces = 1 mithril piece. One has to wonder why they didn't just melt down the copper and tin pieces, mix them together, and sell them as bronze pieces.
A science fiction game example would be Star Ace. All money is "hard currency", coins made of different precious metals.

Video Games

EverQuest has platinum coins above the other three. Each denomination trades up at a 10:1 ratio. The coins don't automatically get converted up; you have to do that at a bank. In EverQuest II, the exchange ratio was increased from 10:1 to 100:1.
Dark Age of Camelot has mythril, platinum, then the other three. Copper trades up to silver and silver to gold at 100:1, gold to platinum and platinum to mythril at 1000:1.
World of Warcraft uses gold, silver, and copper coins at a ratio of 100:1. These rarely appear by name, however; instead, pictures of yellow, gray, and brown coins appear next to the amounts, so a price of 16 gold 47 silver 33 copper would appear as "16 {picture of gold coin} 47 {picture of silver coin} 33 {picture of copper coin}". Exchanges between the various denominations happens automatically; if your character is carrying 90 copper coins and then picks up 20 more copper coins, his inventory will show 1 silver 10 copper (not 110 copper).
Dragon Age: Origins uses the 100:1 ratio. Gold coins are referred to as sovereigns, while copper coins are known as bits.
In Spellforce, the 100:1 ratio applies, but the game doesn't automatically exchange lower denominations for higher when appropriate. This can lead to the player ostensibly carrying around tens of thousands of copper pieces.
Many MUDs would have this as a default setting. The ratios would be juggled slightly: say, 20 silver to 1 gold, 5 gold to 1 platinum.
The Drakensang games use this ratio, but name the coins for historical currencies: the ducat, taler, and farthing. (This can be jarring for players who recognize the ducat, thaler, and farthing, and are expecting them to convert to each other at their historical rates.)
Terraria uses copper, silver, gold, and platinum coins. 100 coins of a lower denomination are equal to one higher-denomination coin. In fact, for ease of storage, 100 coins of a lower denomination can be crafted into a higher-denomination coin. How you craft a lot of copper into a little silver (or silver into gold, etc) is best not thought about too much.
Each town in The Game of the Ages has just one coinage, but the first has copper, the second silver and the third gold.
The Quest for Glory series generally uses a two-coin money system with a decimal exchange rate between the denominations. The games also keep track of the total weight of the player's coins on hand.
- The first game used Silver and Gold coins, with 10 silvers equal to one gold.
- The second game used gold Dinars and copper Centimes, with 100 centimes equal to one dinar.
- The third game used gold Royals and copper Commons, (100 Commons to one Royal).
- The fourth game used gold Crowns and copper Kopeks (100 per Crown).

Web Comics

Tales of the Questor, though the Seven Villages use beads and rings instead of coins as they're in a rather metal-poor region.

Western Animation

The Earth Kingdom in Avatar: The Last Airbender uses gold, silver, and bronze pieces.

Real Life

The coinage of Japan during the Tokugawa period actually used a system much like this with several, large-denomination gold coins (generally oval), a smaller rectangular coin made of silver with a fixed value relative to the gold coins and finally several denomination of smaller copper or bronze coins (circular with a hole in the middle so they could be strung together for convenient transportation).
From 1792 to 1873, the United States Treasury operated on a "bimetallic" standard, where the dollar values of both gold and silver were fixed. The ratio between the two was 15-to-1 until 1834, when it was changed by an act of Congress to 16-to-1; that is, 1 Troy ounce of 24-karat gold was worth exactly the same number of dollars as 15 (or 16) Troy ounces of .999-fine silver. Since the actual value of gold and silver tended to fluctuate on the world market — not only relative to other currencies, but relative to each other — this gold-and-silver standard created a fair share of problems. Ten-dollar gold coins had a special name: "Eagles."