My House Rules on D&D Coinage
Posted by darkstar 11 years ago
A Short Treatise on my House Rules for D&D Coinage  
When I'm playing a game, it never fails that someone will ask a question related to coinage size and weight. Usually, it's when we're trying to figure out how many coins are in that chest we just found in the dragon's hoard, or how much does 1500 silver pieces weigh and can Brother Oen carry them all in his backpack.  
Normally, I try not to sweat the small stuff when handling a game. If it's not critical to the plot, then I tend to make a common-sense ruling and then carry on so as to not get mired into tedious detail. However, sometimes it is necessary to make a simple calculation so that, even in the fantasy realm, a modicum of logical consistency can be achieved. The D&D Rulebooks have a habit of setting forth a regulation for standard coinage that is superficially simple, but not self-consistent. And this lack of self-consistency makes further reconciliation of the size with the mass of such coins actually quite problematic. Thus, this is one of the many areas where, when I manage a game, I institute my own house rules.  
I will hand it to the rulebooks: the latest incarnation of standard coinage in the official rules is better that previous efforts. It still suffers in a number of ways, though, that a house rule can address.  
First, the official rules offer a standard coin size that is usually completely impractical for a medieval economy, fantasy-based though it may be. The standard size, as shown on page 146 of the latest Player's Handbook, measures 1 and 3/16 inches (3 cm) wide. Now, this size of coin may well appeal to fantasy gamers, and in that sense, it's a great idea. But it creates a huge inconsistency in a variety of other areas that confound simplicity. Namely, that amount of precious metal is incredibly heavy in any significant bulk. And furthermore, it's not even self-consistent with the 50-coins-per-pound guideline set forth by the rules.  
A slug of (mostly pure) gold that size, for example, would weigh nearly a full ounce avoirdupois (26.86 grams). If you're trying to figure out how many coins are in a chest of a given volume, and how much those coins weigh, it's easy to see how the game rules actually give you completely incompatible (and insolvable) mass vs volume calculations.  
Second, a chunk of precious metal (silver, for example) that large, while flashy, is hardly likely to be encountered in common trade. It's entirely too large to be practical and one would expect that coins of much smaller size would be in use. Notwithstanding that the fantasy realm can have widely divergent standards, it is usually the case that such simple tropes as the manner of currency trade and precious metals economics are fairly consistent.  
Third, the 50-coin-per-pound rule completely ignores the variable density (a significant difference) for different precious metals.  
It would be helpful to have a standard coin size that was reasonably attested to in history and which could yield reasonable coin masses for various metal compositions. All the better if it is a coin size that is in common circulation, so folks had a tangible example they could see and feel.  
In our own world, for example, Athenian silver "owl" tetradrachms were in common usage for centuries and their size was copied throughout later centuries even after that coin was discontinued. While coins were larger or smaller, they are the average size of coins in common usage. And, in fact, the US 5-cent piece (the "Jefferson nickel") is about exactly the same size: they are struck on blanks 21mm (0.83 inches) in diameter and 1.95 mm (0.08 inches) thick.  
(This is rather thinner than the Athenian owls, but as it turns out, it makes for a mass about that of the Athenian silver stater, the next smaller sized coin in Athenian currency. Overall, this makes for very good standard size of coin.)  
By using a house rule that makes the US nickel the standard coin size in my campaigns, it enables me to have a simple and self-consistent mass and volume for coinage for those times when it's needed.  
For Volume...  
Based on the above dimensions, the volume for a given coin is approximately 675 cubic mm. That converts to 0.675 cubic cm or 0.04 cubic inches. In one cubic foot, therefore, the maximum number of coins (assuming perfect packing with no gaps) is 1728 / 0.04 = 43,200 coins. Because coins do not pack perfectly, assume a conservative one-half volume efficiency for loose coins. Therefore, approximately 21,600 (or more) loose coins will fit in one cubic foot (regardless of the metal) and for our metric friends, 763 coins per liter.  
For Mass...  
Because of the density of metals varies, weights for the coins will also vary. Based on nearly 100% purity (not perfectly achieved, but a close enough approximation), coins would weigh approximately:  
i. Platinum: (d=21.4 g/cm3)(0.675cm3) = 14.45g = ~32 per pound (or 71 per kg).  
ii. Gold: (d=19.3 g/cm3)(0.675cm3) = 13.03g = ~35 per pound (or 77 per kg).  
iii. Silver: (d=10.5 g/cm3)(0.675cm3) = 7.09g = ~64 per pound (or 141 per kg).  
iv. Copper: (d=9.0 g/cm3)(0.675cm3) = 6.08g = ~75 per pound (or 165 per kg).  
Thus, the house rule standardizing coinage on the Athenian tetradrachm model allows a ready sample of the coin size (the US nickel), a reliable volume calculation for bulk coinage and reliable mass calculations for bulk coins.  
These figures aren't generally necessary to deal with for most of a campaign. But every now and then I'll get a question like "how many silver pieces can I fit in my bag of holding and how much would it then weigh?" With this reliable means of calculating coinage mass and volume, you can do a 30-second calculation on a scratch pad and give an answer that is entirely self-consistent and won't destroy the local economy.  
What your players do with those coins once they get them back to town, well, that's their business...  
Fantasy coinage geekery bump.
SpearmintFur: Some nerd should sometime do an economic dissertation on the economics of RPGs.  
It sure as hell won't be me though.
darkstar: Heh, over the years, I've written a number of short glimpses into particular aspects of medieval fantasy RPG trade and economics. They usually take the form of one- or two-page outlines of a particular village's (or region's) economic distinctives for my campaigns. I'm sure most campaign writers have done similar things, too.  
Some of mine include:  
1. The logistics of the local wool trade: buying from regional herds, shearing, wool storage, the wool market, carders, fullers and weavers guilds, taxation, etc.  
2. The use of windfall levies on adventurer's loot as a means to supplement tax revenues.  
3. Purchasing and inventory management for a local inn's food preparation (potato and leek soup, crust of bread, local goat cheese and local ale was the house specialty).  
4. Dues structures and consultation fees in the Scribes and Sages Confraternal Guild.  
5. Employment of seaside salt pans and a noble's local monopoly on the salt trade, trading routes and treaties with neighboring domains.  
6. The inflationary effects of adventurers' loot on a small village following a successful campaign.  
7. Gnomish emerald mining and trade using an emerald-based currency.  
8. Metal coinage standards (see above).  
I'm sure there are others, but these spring to mind. As I say, probably most campaign writers do this kind of thing, too.  
A number of scholarly works are also very helpful in getting a better glimpse of the dynamics, such as The Medieval Village by G.G. Coulton. And historical fiction, like the Brother Cadfael mystery series by Ellis Peters and Pillars of the Earth by Ken Follett have superb treatments of so much of medieval economies.  
I've always been fascinated by trade in medieval and earlier societies. Whenever I travel, I'm always keen to investigate the history of local trade practices. But I'm afraid this is one of those areas where much study pays few practical dividends, however. But it is fun (well, to me...)
clu: Dragon Magazine just called. They want you in for your second interview this afternoon.
clu: i. Platinum: (d=21.4 g/cm3)(0.675cm3) = 14.45g = ~32 per pound (or 71 per kg).  
ii. Gold: (d=19.3 g/cm3)(0.675cm3) = 13.03g = ~35 per pound (or 77 per kg).  
iii. Silver: (d=10.5 g/cm3)(0.675cm3) = 7.09g = ~64 per pound (or 141 per kg).  
iv. Copper: (d=9.0 g/cm3)(0.675cm3) = 6.08g = ~75 per pound (or 165 per kg).
What about brass and electrum pieces?  
BTW, I look forward to reading "Darkstar's Ruby and Emerald Guide o'Fortune"
darkstar: Summary answer:  
Electrum: 45 coins per pound (or 100 per kg).  
Brass: 80 coins per pound (or 177 brass coins per kg).  
Bronze: 75 coins per pound (or 165 per kg) - same as copper.  
I don't tend to use electrum and brass coins, but it could come in handy for a game. An efreet trove, for example, would be a great place for a hoard of brass coins. A chest of electrum coins would be a good ancient king's burial trove to uncover.  
Electrum and brass are alloys that vary widely in composition, and they don't lend themselves to nice powers-of-10 calculations of value, compared to other coins.  
However, if I were to standardize electrum, I'd probably use a 50%/50% gold:silver composition for electrum. That's in line with the earliest electrum coinage percentages and it makes calculation easier, too. Such a coin would have a density of 14.9 g/cm3, with a mass of 10.06g. Thus, 45 electrum coins per pound (or 100 per kg).  
If I were to standarize brass for coins, I'd probably use an "alpha brass", which has 70% copper to 30% zinc. This would give a nice, lustrous golden yellow color, but still allow adequate malleability for cold-striking coinage. This is substantially the same as cartridge brass. The density of such a coin would be 8.39 g/cm3, with a mass of 5.66g. Thus, 80 brass coins per pound (or 177 brass coins per kg).  
In many cases, the "brass" coins used in antiquity weren't actual brass (an alloy of copper and zinc), despite that term appearing in ancient texts, but what we today would call "bronze" (an alloy of copper and tin). The earliest coins of the Roman empire, for example, were bronze and bronze was used for Greek coins, as well. References in the Bible to "brass" items and such are almost certainly referring to copper or bronze and not actual brass alloys.  
So it may be that bronze coins would be more in keeping with ancient coinage. However, in many ancient bronze coins, the alloy also included a small percentage of lead, as well, to facilitate striking. In settling on a bronze coin composition, the proportion of less-dense-than-copper TIN used thus could be balanced out by the more-dense-than-copper LEAD present, so that a bronze coin could have very similar density to a pure copper coin. As a result, without trying to get into the details of percentage compositions, I'd just consider a bronze coin to be the same density and bulk mass as a copper coin: 75 per pound (or 165 per kg).  
clu: What's your stance on multiple currencies? I imagine the size of coins would naturally differ between different regions, and most likely between different races.  
And what about rare coins from ancient civilizations? I suppose I would play it so that those unfamilar would overlook their significance. To learn the true value would require someone specialized in ancient currency.
darkstar: I think that's when I'd tend to use electrum, brass and bronze, as well as perhaps oversized gold coins, etc. I don't tend to use those in my games, so they'd make good "foreign" currency to introduce if you needed to do so.  
Hence, the idea of a brass coin trove from an efreet cloud castle or a chest full of electrum pieces in an ancient tomb. Possibly, nice, fat gold or platinum coins of exceptional size as a special find.  
I have used ingots as trading currency between kingdoms, as well. Specifically, where a crate of 5-pound platinum ingots was being transported as tribute from one king to another. Ingots would have a 10% reduced conversion rate because they need to be minted, yet. But it adds a bit of variety to the old chest of coins trove.  
I'm also partial to jewels and gemstones and other valuables as a way to spice up treasure finds. Bilbo's silver casket full of silver pieces is much more dramatic than just a sack full of silver coins. A golden flagon with garnets encrusting the outside is much cooler, imho, than a similar value of loose coins. A large star sapphire set in a platinum amulet, a silver chalice, a fine silk-lined dragonwood chest, a tapestry of silver and gold threads, a crystal container holding a rare spice...all of those add a special flavor to a treasure find.  
I also like to add the occasional simple magic item that is very practical: an agate cup that creates a cup of water 5x per day, a pair of firestones (bits of clear crystal which, when in contact with each other, will heat up to the point of setting paper on fire, boiling water, etc.), a feather quill that is everfull of ink, a length of magic string that, when broken, emits a loud "pop!", etc. Simple things that don't have too much sales value, but add to the charm of a world where magic is used and, in the hands of the resourceful, can be used to do some neat things in the game.  
I try not to overdo it with that kind of embellishment, but those little touches can add pizzazz (and imagery) to what might otherwise be simply another clinical loot-and-scoot, as well as encouraging more inaginative game play.
tl; dr
lorddimwit: tsia
darkstar: np  
You're supposed to be focusing on other reading material, anyway! Get back to work!  
Darwish: I totally read all of that.