Most of the gaming systems, such as Dungeons and Dragons, use a pricing system based around copper, silver, and gold coinage, artificially set at a ratio of 100:10:1 (such that 10 'coppers' equals 1 'silver', and 10 'silvers' equals 1 'gold'). For instance, the d20v3.5 Player's Handbook lists a mug of ale as worth 4cp (copper pieces), a sheet of paper as worth 4sp (silver pieces), and a set of custom-tailored full-plate armor as worth 1,500gp (gold pieces).
The older, 2nd Edition Player's Handbook indicated that 5 gold pieces were worth 1 platinum piece, and that 5 silver pieces were worth 1 electrum piece, or something along those lines. (I don't have one of the books handy, so if you know the exact values, shoot me an e-mail -- it's listed on the main page.) The newer editions of Dungeons and Dragons have dropped the confusing electrum and platinum pieces concepts, and stayed with a greater, more simplified system.
The Warhammer system tends to use coinage at a 20:20:1 ration, rather than a 10:10:1 ratio. Gaeleth explicitly uses a 10:10:1 ratio, regardless of gaming system.
In general, currencies are confusing; most people don't know the value of a 'Gold Certified Dollar', or understand the historical underpinnings of the gold-to-silver exchange rates. Rather than make a musty and dry historical introduction to currency, I'm going to try and introduce some in-game concepts that can help liven up those Dungeons and Dragons players that are interested in a more realistic form of game-play with precious metals.
So how much does a sack of gold coins weigh? There are a lot of variables in that question, from the sizes of the cold coins to the number of coins in the sack -- and if it's a leather sack strong enough to hold a fair amount of gold, then the sack itself must weight some considerable amount. For the sake of adventuring brevity, most Dungeon Masters merely indicated, "There are 4,500 gold pieces, 6,000 silver piees, and 14,000 copper pieces." To which the players usually respond, "Yeah!" and deal with getting the coins into town by saying, "We load it all up, and go back to town!"
For a computer game, it works well enough, where the amount of gold a person is carrying is never considered into their weight or encumbrance. I tend to like a little more realism in my games, and go so far as to figure out the particular eras in which the coins were minted. While I like some detail, I don't want to bore my players to death, so most of the coinages have been standardized through the use of the in-game gods. (For more information, see the entry on Lul, the God of Merchants.)
A recent acquisition at the Houston Museum of Natural Science and Industries introduced me to replicas of historical coins, thanks to the UK Ancestors company (www.ancestors.co.uk), in the Timeline category of products. Many of the replicas were much smaller than I had anticipated, but make sense in a historical context. For example, the 'half crown' of England's James VI is the size of two American pennies stacked atop one another, or approximately 18mm in width and 2.5mm in depth.
Quick and boring math: a cylinder of 0.9cm radius and 0.25cm height is 0.636cc (cubic centimeters) in volume. Gold has a density of approximately 19.3g/cc, so a James VI half-crown of (nearly) solid gold would weigh about 12.27 grams. While we know they were not 100% pure gold, and usually contained some copper to harden them, as much as 10%. 1. This puts the weight of a half-crown's gold during 1604-1625 at around only around 9.2 grams (out of the 12.27 grams coin weight), with the remainder in copper, as a hardener.
Silver coinage in Brittain was often defined by the 'pound sterling', or 240 pennies of sterling silver (93% silver, 7% copper). A 'penny' weighed approximately 1.5 grams in 1000AD, and only half a gram by around 1600AD as currencies shifted in valuation. 2. One 'troy ounce' is approximately 31.1 grams.
If the value of the silver coin is fixed to the value of the gold coin at a 10:1 ratio, as mentioned in the Player's Handbook, then we find the silver coin's weight set at three-quarters of the gold coin's weight. 3. Ironically enough, because of the impurities of the gold and silver (the adding of copper to harden them), this sets up the actual gold-to-silver ratio at 1:13.3 -- but it's never actually needed in a Dungeons and Dragons universe if gold and silver coins are standarized so that all the coins have the same amount of gold and silver in them, and weigh roughly the same.
A silver coin on Gaeleth would weigh 9 grams, and be about 24.3mm in diameter with a 2.5mm depth; 8.1 grams of the coin is pure silver, the rest being copper as a hardner. The silver coins of Gaeleth are about half a centimeter wider in diameter than the gold coins, and yet weigh only three-quarters as much as the gold coins. There are about 50 silver pieces in a pound, and a thousand such silver pieces weighs 19.84 pounds.
Copper pieces on Gaeleth might be linked to silver at a 10:1 ratio, but like gold and silver, the actual exchange rate would probably be different. Copper coins throughout Gaeleth are set at 3/4 the weight of the silver coin, and this makes them 6.75 grams, 2.34cm in diameter, and 0.175cm in depth -- the same depth as a silver piece, one half the depth of a gold piece, and almost an inch in width. Like the silver and gold coins, they are tempered with some hardening alloys and other metals to reduce their purity, so pure copper actually trades at a rate of 20:1 to pure silver.
Gaeleth coinage standards:
1,000gp weighs 26.5lbs
1gal holds roughly 5,951gp, and weighs 158lbs
The shapes of the coins can vary by era and by nation. For instance, the Vridaran Empire uses triangular coins known they call 'chits'. Some nations use square coins, or coins with holes in the middle. Whatever the age of the coins, unless they have been 'clipped' illegally, the coins should be of roughly standardized value.
2. pierre-marteau.com entry for "Money (Great Britain)", Author and Date of posting Unknown.
3. "Money, Currency, Precious Metals" by Dr Gérard P. Michon, 'Final Answers' at Numericana dot com, (Original posting date Unknown).
4. "The Gold / Silver Ratio Strategy and the Case for Silver" by F. Sanders in The Moneychanger March 5, 2003.
24carat.co.uk's Density List, Author and Date of Posting Unknown.
"Money in Ancient Times" by (Author Unknown), Oesterreichische Nationalbank (OeNB)'s online historical pages, (Date Unknown).
TaxFreeGold dot com's 'World Gold Coins' collection, Author and Date of Posting Unknown.