How big is the 2g bit copper coin of ‘The Hero of the Valley’?

The author Gary Spechko has started a Lit RPG series called “The Hero of the Valley” and in it, he has the usual 100 coppers to a silver and 100 silvers to a gold setup. In the book, on page 138, he also states in the text how much a bit, the one copper of this currency, weighs. In his fiction it weighs 2 grams, considerably less than the 9.45 gram coins of D&D. So what are the dimensions of this coin and how does it compare to some lightweight real coins?

The lightest coin in use by the US Government was the trime, the three penny silver coin. It was 75% silver and 25% copper and was popular when postage stamps cost three pennies. It was 14 mm in diameter and with 75% silver, I can estimate the thickness of the coin as about 0.514 millimeters. Later versions shifted to coin silver (90% silver and 10% copper) and grew lighter, but for now, this is what we can start with.

I will assume the bit is as thick as the American dime. The bit is substantially heavier than the trime, and the diameter calculates to be 14.5 mm, if the coin is pure copper. The dime by contrast, has a radius of 8.95 mm and so its diameter is 17.9 mm, larger than the trime and the bit. If you adjust the thickness of the bit to 1.0 mm, then the bit has a radius of 8.43 mm, almost matching the radius of the dime.

I’ll note that through most of the 18th century and before, the pence was a silver coin, not copper. This use of copper as a “medieval” currency is a RPG convention not rooted in history. Now the US penny, first made in 1787 was a copper coin but it’s hardly medieval. It was only in the 20th century that nations began to create legal tender, not connected to any metal standard. Copper just wasn’t worth enough in medieval times to stand alone as currency of any kind.

How big are the coins of D&D?

I’m going to say up front that I prefer these days to think and work in a magical environment whose coinage is modeled after the coinage of Great Britain around 1720. This is one where there are twelve coppers per silver, twenty silvers to the “gold” (the gold piece being a coin containing 111.4g of silver) and the worth of the gold coin, the guinea (7.6885g fine gold), Isaac Newton in 1717 set to a value of 21 silver shillings, not 20, and setting the base gold to silver ratio to 15.2 to 1.

Base 240 systems have some virtues in a pre-calculator era. One third of a gold can be made exact, it’s 80 copper. In an era where people clipped coins in half, quarters, or bits, to make change., base 240 worked well.

Because the worth of copper in the 1700s, around 80 ‘gold’ a ton, was not high enough, in those days the “copper” penny contained silver.

D&D coinage is discussed well enough here. Coins are a third of an ounce. If you divide weight by density, you get volume. Just as a comparison, a US quarter is 809 cubic millimeters in volume. The corresponding densities of copper, silver and gold are 8.92 g/cc, 10.5 g/cc and 19.3 g/cc respectively. This gives sizes of D&D coins as follows: 1059 cubic millimeters (cu mm) for copper, 900 cubic millimeters for silver, 489 cubic millimeters for gold. The gold coin is smaller than a US nickel (688 cu mm) but bigger than a US dime (340 cu mm). Platinum has a density of 21.45 g/cc so a platinum coin would have a volume of 441 cu mm.

Some notes on electrum. This is a naturally occurring alloy of silver and gold that typically has 70-90% gold. A pure electrum coin should be worth more than the D&D equivalent. The electrum coins were the first coins, used in Anatolia. That said, most coins were alloyed with silver to give 45-55% gold, which jibes with the D&D simplification that one electrum = 5 silver.