D&D 5E Coin sizes

[MechaPilot]

What if a "copper piece" is just a value, and you can pay that value with a copper coin the size of a US Kennedy Dollar, with a silver coin the size of a US nickel, or a gold coin the size of a US dime?

 

[PeterFitz]

I worked out coin sizes a little while ago with the aid of Wolfram Alpha:

These sizes assume a coin thickness of 2mm, at 50 coins to the pound. If you want to use a 100/lb ratio, just drop the thickness to 1mm and Bob's your uncle.

 

[77IM]

PeterFitz, that's excellent! Thank you for sharing!

 

[The Grassy Gnoll]

Electrum keeps trying to blag to girls at parties that he's "with the band", but everyone knows he's just jealous of his sexier and more musical cousin, plectrum. It's why he drinks.

 

[aramis erak]

Quibble over the details...

Platinum, pure 21.4 g/cc
Gold, 24k, 19.6 g/cc
silver, 0.999fine, 10.49 g/cc
Copper 8.9 g/cc
tin 7.2 g/cc
zinc 7.31 g/cc

Electrum is a problem - it has 2 common formulations which are gold & silver alloy... but it's defined as 20-80% gold and 20-80% silver, with the balance in base metals (copper, tin, zinc, antimony)

• Lycean: 45-60% gold 35-55% silver, 0-5% base metals
• Anatolian: 70-90% gold, 9-30% silver, trace base metals
• German: 60% copper, 20% tin, 20% zinc

Coin gold is typically 14k, (58%,) with the balance being copper, and a specific gravity of about 15.1g/cc. Lets call this our base worth for gold coin... which is a good thing, since pure gold (24k) is worth about 12 to 20x silver... and this gives about 1 15.5:1 ratio to the silver coin, and thus pure gold worth about 1.55x coin gold

Coin Silver is usually 90% silver, the balance being largely copper; pure silver doesn't wear well enough. Some medieval silver coinage was as low as 50%, usually mixed with tin, zinc and copper. 90% is about 10.4 g/cc... 50% is about 9.7 g/cc

Coin Copper, is almost always alloyed with tin and zinc, and sometimes with gold or silver. But copper's inherent value is about 1/70th that of silver in the medieval era. So, to plus it up, say, 5% silver... if we go with 90 copper, 7.5% silver, 2.5% zinc, we get about the right value, about the right hardness, and about the right brightness, and a historic coin composition. We also get about 8.98 g/cc

Note that the platinum coin, given the generally medieval tech, is anchronistic, and would require magic to work. (developing the ore isn't the problem, despite being essentially victorian; actually working it, however...) So, assuming nearly pure is fine. Setting the value to 10x gold (rather than the current 0.9x) is thus easily justified.

And, for electrum, let's go really debased... 27% gold (worth 0.419 gp), 70% silver (worth 0.07 gp) 3% copper. It's about 12.8 g/cc and worth just shy of half a gp

So, recapping more realistic coin-densities, and 9.07g per coin. 3 figure accuracy

Platinum coin (magically pure)	21.4 g/cc	0.424 cc	23.2x1mm	19.0x1.5	16.4x2mm
Gold Coin Alloy 14k	15.1 g/cc	0.601 cc	27.7x1mm	22.6x1.5mm	19.6x2mm
Low Gold Electrum 0.27/0.70	12.8 g/cc	0.709 cc	30x1mm	24.5x1.5mm	21.2x2mm
Coin Silver Alloy .900 fine	9.7g/cc	0.935 cc	34.5x1mm	28.2x1.5mm	24.4x2mm
coin copper alloy (5% silver)	8.98 g/cc	1.01	35.9x1mm	29.3x1.5mm	25.4x2mm

1.01 cc[/td]

 

[Cadriel]

50 coins per pound is a good standard. It gets you coins not unlike a U.S. quarter, which are substantial without being ridiculous (the 10 coins to a pound standard results in coins heavier than a U.S. silver dollar by 50%). Going to 100 coins per pound gets you a coin like the Roman denarius or the Byzantine solidus, which are smaller. I have several ancient denarii, and they compare to dimes, while later coins like the antoninianus (infamous for its debasement; my antoniniani are all heavily blackened) are more physically impressive in size.

So I think 5e is in the Goldilocks zone for fantasy coins.

 

[mlund]

Also, I am starting to think that for 5e they should have thrown out the sacred cow of "50 coins = 1 lb." and gone with the more decimal system of "100 coins = 1 lb."

They should have because it is closer to the classical / middle-ages norm and more convenient. The real-world "Gold Piece" standard of the middle ages was the Roman Solidus, produced by the Roman Empire (Byzantine Empire in modern parlance) in Constantinople. The Solidus originates as a coin of the purest form of gold that could be obtained in a weight of 1/72th of a Roman Pound. The Roman Pound just happens to be 0.72 British/American Imperial Pound. So 100 Classical Solidi is 1 Modern Pound of Gold.

Marty Lund

 

[Cadriel]

They should have because it is closer to the classical / middle-ages norm and more convenient. The real-world "Gold Piece" standard of the middle ages was the Roman Solidus, produced by the Roman Empire (Byzantine Empire in modern parlance) in Constantinople. The Solidus originates as a coin of the purest form of gold that could be obtained in a weight of 1/72th of a Roman Pound. The Roman Pound just happens to be 0.72 British/American Imperial Pound. So 100 Classical Solidi is 1 Modern Pound of Gold.

Marty Lund

The solidus is a fine coin. It's about the size of a dime, weighing around 4.5 grams. Its weight is equivalent to the denarius, though due to relative density it's thinner.

The problem with those two coins as standards is that they're quite small. When you imagine a fantasy treasure chest, you don't think of it as full of little dime-sized coins; it has coins with a bit more heft and substance. 9 gram coins are much better; a gold piece that looks like the US dollar coins is a more appealing imaginary treasure. It's not 1e's silly 45 gram standard, where the coins would come out massive.

Really, coins should vary. Actual gold coins were from 3.5g up to more than 10, and some famous silver coins like the Spanish "Piece of Eight" we're big whoppers at over 25g. It can add color to have little or big coins, as long as you consider the overall value based on weight and metallic composition; you could give 36 GP in 72 late Roman solidi, if you wanted.

 

[77IM]

Ah, but that's where MechaPilot's fine idea comes into play:

What if a "copper piece" is just a value, and you can pay that value with a copper coin the size of a US Kennedy Dollar, with a silver coin the size of a US nickel, or a gold coin the size of a US dime?

If standard coins are tiny, then you can have coins of the same metal, but one denomination up, and they are only 10x as massive -- which, due to width*pi*r^2, means they are not 10x in diameter, but still fill up a treasure chest nicely!

So now, a merchant may have a few dime-sized gold pieces and nickel-sized silver pieces in his money-purse, but a dragon is laying on a bed of "gold pieces" made of giant silver coins and "platinum pieces" made of giant gold coins. Shiny!

 

[MechaPilot]

Really, coins should vary.

As I see it, not only should coins vary, but currency itself should vary. As should the value of various coins and currency.

In my homebrewed campaign setting, called Tenesia (after one of the major land-masses of that world), coins vary in size, shape, character, and value:

One nation mints its coins with the profile image of its current ruler (if you know the history of that nation, you can tell the age of a coin by the ruler depicted upon it).

Another nation mints coins with animals depicted on them (eagles, wolves, buffalo, etc).

Under the sea, the merfolk don't get coinage unless it comes from wrecked ships. Coins are as valuable to them as gems are to those who live above the waves. Instead, they have a system of currency based on sea shells, shark teeth, and pearls.

For the races that live underground, precious metals are cheap. The price of anything is inflated if you try to pay for it with gold, silver, and copper. Instead, they frequently make their valuable coinage from rare alloys, or pay for things with gems (which are still more rare and valuable than gold, silver, and copper).