How Many Coins Can You Lift?
For convenience, we assume all coins weigh the same. But how heavy is a FRPG coin in real-world units of mass?
In Shadowdark 100 coins occupy a Gear Slot, although the first 100 don’t count. D&D 5e uses pounds; 50 coins weigh a pound, which means each coin weighs 9.07 grams.
However, these are heavy coins. The historical denarius and drachma weighed about than half of that, between 4.3g (source) and 4.6g (source), with denarii growing smaller and less silver all the time. The sceat, predecessor to the English silver penny between the 5th and 9th centuries A.D., weighed only between 0.8g and 1.3g. (source) The modern British pound coin weighs only 8.75g. (source) Only the modern American half-dollar, rarely used, weighs more than our fictional coins, at 11.340g. (source)
If we assume each coin weigh 5 grams or less, maybe each Gear Slot should carry 200 coins. That still gives us a respectable kilogram of weight, with each character able to carry at least 10 Gear Slots worth of Gear without suffering any “encumbrance” penalties. (Or 11, if we count the free gear slot full of coins.)
For reference, the U.S. nickel weighs 5.00 grams. (source)
How Many Silvers in a Gold?
As argued here and here one can and probably should convert the gold standard in most FRPGs to a more historically accurate silver standard, i.e. all prices stated in silver pieces, with gold coins worth at least 20 silver. For example, the Achaemenid Empire defined 20 silver sigloi equal to one gold daric. I can’t find a reference for the weight of a siglos, although one page referred to the sigloi as a shekel (at least 11.4 grams), which would make it heavier than the listed mass of the daric (8.4g). That puts the ratio closer to 26 to 1.
In previous articles I’ve argued that a better ratio would be 100 silvers to one gold. Not only is the math easier, it more accurately reflects modern gold and silver prices, which currently stand at a ratio of about 85 to 1. But there’s no reason apart from easier math that gold and silver (and copper) coins should all weigh the same, or even that coins of the same metal from different kingdoms should all weigh the same.
Smaller Coins and Dwarf Currency
When I came up with Myrkheim I decided that the Dwarfs have their own weights and measures. Originally I decided that a Dwarf Gold Guilder has the same value as two “pounds” of silver. Dwarfs divide each pound of silver into twenty “thalers”, and each thaler consists of a number of silver pennies such that each penny is between one and two grams. I used the standard American pound of 453.59 grams, which gave me 15 pennies per thaler; each penny weighs about 1.52 grams.
Revising the weight of a silver piece to exactly 5 grams allowed me to make the math work out more neatly:
- By pure coincidence, Dwarfs use metric weights. Their pound is a “metric pound”, i.e. half a kilogram.
- Dividing the kilogram by 40 means that each thaler is now exactly 25 grams.
- If we assume 20 pennies in a thaler, we arrive at a penny weight of 1.25 g.
- With our revised estimate of a “silver piece”, that means that there are four pennies per silver piece, not six.
- Meanwhile, the human kingdoms still use a gold “crown” with the same weight as their silver and copper pieces, i.e. 5 grams.
This is how all the currencies work out now:
| Coin | Weight (g) | Weight (sp) | Value (sp) |
|---|---|---|---|
| Myrkheim gold hundred thaler | 25.00 | 5 | 500.000 |
| Myrkheim gold guilder (G) | 10.00 | 2 | 200.000 |
| Myrkheim pound of silver (£) | 500.00 | 100 | 100.000 |
| gold crown (gc) | 5.00 | 1 | <100.000 |
| Myrkheim silver thaler ($) | 25.00 | 5 | 5.000 |
| Myrkheim silver tenpence | 12.50 | 2½ | 2.500 |
| Myrkheim silver fivepence | 6.25 | 1¼ | 1.000 |
| silver piece (sp, s) | 5.00 | 1 | 1.000 |
| Myrkheim silver tuppence | 2.50 | ½ | 1.000 |
| Myrkheim silver penny (d) | 1.25 | ¼ | 0.250 |
| copper piece (cp, p) | 5.00 | 1 | 0.100 |
Coin Dimensions
Worried that these fantasy coins were too small to be usable, I whipped up a quick spreadsheet to estimate how big they actually are. With some guesstimates of coin thickness, here are the results:
| Name | Metal | Weight (g) | Thickness (mm) | Density (g/cm3) | Diameter (mm) |
|---|---|---|---|---|---|
| old silver piece | silver | 9.07 | 2.000 | 10.49 | 23.46 |
| old gold crown | gold | 9.07 | 2.000 | 19.30 | 17.30 |
| new silver piece | silver | 5.00 | 2.000 | 10.49 | 17.42 |
| new gold crown | gold | 5.00 | 1.500 | 19.30 | 14.83 |
| Myrkheim guilder | gold | 10.00 | 2.500 | 19.30 | 16.24 |
| Myrkheim penny | silver | 1.25 | 1.500 | 10.49 | 10.06 |
| Myrkheim thaler | silver | 25.00 | 2.000 | 10.49 | 38.95 |
| aureus | gold | 10.00 | 2.000 | 19.30 | 18.16 |
| denarius | silver | 5.00 | 2.000 | 10.49 | 17.42 |
The following expression calculated diameter:
20 * sqrt( 10 * (weight) / ((thickness) * (density) * PI) )
Assuming I didn’t mess up my algebra or unit conversions, these figures put the 9 gram silver piece as about the size of a U.S. quarter, and the 5 gram silver piece about the diameter of a U.S. dime. The 9 gram gold crown is about the size of the 5 gram silver piece because gold is nearly twice as dense as silver.
The Myrkheim thaler is the same size as the Early Modern Spanish Dollar. I made the Myrkheim guilder thicker to approximate the old British pound coin, but there simply wasn’t enough metal to go around.
The Myrkheim penny is only about half the circumference of a U.S. cent. It is modeled on the English sceat, though, which look tiny in photos. It’s also comparable to the mass of an Ancient Greek diobol, which was also pure silver. I guess coins that small were acceptable back then.
The aureus and denarius aren’t really based on the historical Roman coins, but they demonstrate that in the real world one would make a gold coin close to the same dimensions as a silver one, just twice as heavy.
So What’s The Point?
First, I’m a little mystified how D&D 5e got the “50 coins per pound” figure, unless it was a compromise from even more unrealistic weights in earlier editions. 200 coins per kilogram seems much more reasonable.
Second, the weight (and the amount of silver) in a silver coin has varied throughout history, from the incredible shrinking denarius through the sceat right until the present day when our coins have no silver at all. In a game it’s convenient to assume every silver coin contains the same amount of silver, but in reality the Greeks, Romans, Persians, and other major civilizations of the Classical Period used different weights and measures. The ancient world converged on 4.5 grams, but that’s just as arbitrary as 5.00, 9.07, or 10.0.
Especially in a game of imagination, as long as everyone agrees on the same values and ratios, the game will play just the same. (Compatibility with third-party products might be an issue, but the adjustments are simple.) There are even RPGs that don’t bother counting coins at all: the game uses an abstract “Wealth” number, or “Credit Rating”, or some such.
Perhaps I’m so insistent on my silver-based, gold-is-for-the-wealthy system because I expect a certain amount of verisimilitude even in my elf games. When I make some back of the envelope calculations, whether it’s probabilities, the weight of coins, or the proportions of metals, I expect that the numbers make some sort of sense.
In the real world gold is rare, silver less so, and copper incredibly cheap. A coin of 9 or 10 grams is less convenient than one that’s two to five grams. In my imaginary worlds unless stated otherwise the same constraints apply, and therefore imaginary people would do what their historical analogues have done: smaller and more varied coins, with gold coins far more valuable than silver, and lesser metals valuable only valuable when backed by a powerful nation-state.
I would expect game designers to do the same back-of-the-envelope calculations I’ve done before they publish. Is that so much to ask?