D&D: How Big is That Gold Coin?

After an earlier article about economics (see D&D: How Much for That Sword?) I looked into the actual values of metals and coins—a huge topic to be sure. There are plenty of articles on the subject, including this one which I thought was the most complete (click here: Gold & Silver Coinage in Fantasy/Medieval RPGs, by Charles D. Hail ©2010). I’m sure you’ll find more. Given the plethora of well-written material, I didn’t feel compelled to reinvent the wheel.

            On the other hand, along the lines of obscure and largely useless knowledge, there is a remaining point that hasn’t been looked into, as far as I know. If we're cool with the game’s premise, a D&D BECMI coin weighs 1/10^th of a pound. It doesn’t say what kind of coin though, therefore one must assume that All coins weigh the same, since coins are also the standard measure of encumbrance (cn). I bet you can already see where I’m going with this.

            If the coins all weigh the same, their physical sizes must differ because metals have different densities (you knew that, right?): gold is heavier than silver, and silver outweighs copper, etc. Out of curiosity, I wanted to find out approximately how big a bag of 1,000 coins should be, depending on the coins. I think I got the math right, but please do correct me if I goofed. Thank you.

Assumptions: The contents of a bag form an approximate sphere. About 20% of the space inside a bag is empty because old coins are somewhat rough edged, some may bulge, or they lie inside the bag at different angles. The coin volumes come from calculators you can find on Google. Bag sizes express the contents’ approximate diameter. So, at 9” across, a bag is assumed to be full and taller than it is wide, possibly 9x15 overall.

Coin Sizes (all weighing 1/10th pound)
Coin Type	1 Coin			1,000 Coins
	Volume	Diameter	Thickness	Bag Capacity	Bag Size
Copper	5,074 mm³	37.9 mm	4.5 mm	6,088 cm³	23 cm
		1.49 inch	0.18 inch		9 inches
Silver	4,321 mm³	37.1 mm	4 mm	5,185 cm³	21 cm
		1.46 inch	0.16 inch		8½ inches
Gold	2,352 mm³	31.6 mm	3 mm	2,823 cm³	18 cm
		1.24 inch	0.12 inch		7 inches
Platinum	2,112 mm³	29.9 mm	3 mm	2,535 cm³	17 cm
		1.18 inch	0.12 inch		62/3 inches

            So, all things considered, that copper coin is pretty large compared with a US quarter (24 mm across or just under an inch) or its thickness (2mm, or 0.08 of an inch). At 4.5 mm thickness, it’s a chunk, but despair not: plenty of coins in the real world were thicker than this. Take for example Russia’s 1771 copper coin (the “Sestroretsk” rouble; see below) measuring 78mm diameter and a whopping 35mm thickness. That’s not a coin, it’s a paperweight! You can kill someone with that.

            The funny thing is, a 6.66” bag of platinum coins technically has the same “encumbrance” as a 9” bag of copper coins, since they weigh the same—according to D&D game mechanics at least. Thought you might want to know about this obscure and largely useless fact.