Originally posted https://www.reddit.com/r/DnD/comments/8ctupf/the_size_of_coinage_in_dd_5e/
While 5E specifies a weight for coins, it doesn't specify size. This makes sense, since if coins all weigh the same amount, their sizes necessarily change based upon their differing metal content. Additionally, it is indicated that there are a number of different shapes of coins in use in the world, and shape can wildly change size, depending what variables you attempt to maintain. While in real life, anything other than round is very rare in regular issue pre-modern coinage, I thought it would be nice to produce some tables of what sizes coins would be in assorted shapes and metal compositions.
If you’re minting a coin of a specific weight, there are three other basic factors in play: Size, Shape, and Thickness. You can standardize any two of those at a time, but the third will have to change if the metal changes, since different metals have different densities, and a will require more or less volume to achieve a given weight standard. The following are tables for the resulting dimensions when you make coins of specific shapes, standardizing either the size of each coin (makes for easier stacking) or the thickness (makes for easier identification).
Circular Coins
The standard shape of coins the world over, since physics pretty much makes this the natural shape resulting from the minting process. The gold piece in either of these options is very close in size to an American one cent coin.
The standard shape of coins the world over, since physics pretty much makes this the natural shape resulting from the minting process. The gold piece in either of these options is very close in size to an American one cent coin.
- If all your coins all have a thickness of 1.5875mm (1/16”), then their diameters will be:
CP: 28.45mm (1.12”)
SP: 26.42mm (1.04”)
EP: 22.35mm (0.88”)
GP: 19.30mm (0.76”) <-- About the size of a US penny
PP: 18.288mm (0.72”) - If all your coins are a matching 20mm (0.79”) in diameter, then their thicknesses will be:
CP: 3.23mm (.127”)
SP: 2.75mm (.108”)
EP: 2.01mm (.079”)
GP: 1.50mm (.059”)
PP: 1.35mm (.053”)
Square Coins
While square coins exist in various nations around the world, they were extremely rare prior to the widespread use of machine minting. Examples from medieval Europe tend to be siege coins and emergency issues, which were physically sliced from a sheet of metal in the absence of proper minting equipment. Because squares maximize volume, these see the greatest extremes in size change across metals.
While square coins exist in various nations around the world, they were extremely rare prior to the widespread use of machine minting. Examples from medieval Europe tend to be siege coins and emergency issues, which were physically sliced from a sheet of metal in the absence of proper minting equipment. Because squares maximize volume, these see the greatest extremes in size change across metals.
- If all your coins all have a thickness of 1.5875mm (1/16”), then the length of their sides will be:
CP: 25.16mm (.99”)
SP: 21.46mm (.84”)
EP: 15.61mm (.61”)
GP: 11.66mm (.46”)
PP: 10.49mm (.41”) - If all your coins have a matching 20mm (0.79”) side length, then their thicknesses will be:
CP: 2.53mm (.10”)
SP: 2.16mm (.09”)
EP: 1.57mm (.06”)
GP: 1.18mm (.05”)
PP: 1.06mm (.04”) <-- This is wafer thin, but coins this thin did exist
Triangular Coins
While modern triangular coins do exist (typically as special commemoratives designed for the collector market), I’m not aware of any medieval coins minted in this shape. Many wedge-shaped pieces of coins were used (the famous “pieces of eight” for example), but these tended to be round coins that were then sliced up like a pie in order to make change. When the value is in the metal itself, the “coin” itself is more a convenient means of identifying a quantity, and fractions of it retain their fractional value perfectly. These calculations are for equilateral triangle shapes. If you’d prefer a right triangle, use the tables for squares, and double the thicknesses.
While modern triangular coins do exist (typically as special commemoratives designed for the collector market), I’m not aware of any medieval coins minted in this shape. Many wedge-shaped pieces of coins were used (the famous “pieces of eight” for example), but these tended to be round coins that were then sliced up like a pie in order to make change. When the value is in the metal itself, the “coin” itself is more a convenient means of identifying a quantity, and fractions of it retain their fractional value perfectly. These calculations are for equilateral triangle shapes. If you’d prefer a right triangle, use the tables for squares, and double the thicknesses.
- If all your coins all have a thickness of 1.5875mm (1/16”), then the length of their sides will be:
CP: 38.40mm (1.51”)
SP: 35.47mm (1.40”)
EP: 30.27mm (1.19”)
GP: 26.15mm (1.03”)
PP: 24.82mm (0.98”) - If all your coins have a matching 20mm (0.79”) side length, then their thicknesses will be:
CP: 5.86mm (.23”)
SP: 5.00mm (.20”)
EP: 3.64mm (.14”)
GP: 2.72mm (.11”)
PP: 2.45mm (.10”)
Hexagonal Coins
A number of coins over time have been standard polygons of more than four sides. Anything from five to twelve sides isn’t unheard of. The more sides are added, the easier it actually becomes to make, because the shape gets closer to the natural round one that metal wants to form when pressed. Anything above six sides I would probably just use the “round” table and estimate from there (an octagon, for example, has an area only about 10% smaller than a circle of the same diameter. A decagon is about 5% larger, and a dodecagon is about 2.5% larger). The distance from one point of a hexagon to the far opposite point is called the “long diagonal.”
A number of coins over time have been standard polygons of more than four sides. Anything from five to twelve sides isn’t unheard of. The more sides are added, the easier it actually becomes to make, because the shape gets closer to the natural round one that metal wants to form when pressed. Anything above six sides I would probably just use the “round” table and estimate from there (an octagon, for example, has an area only about 10% smaller than a circle of the same diameter. A decagon is about 5% larger, and a dodecagon is about 2.5% larger). The distance from one point of a hexagon to the far opposite point is called the “long diagonal.”
- If all your coins all have a thickness of 1.5875mm (1/16”), then length of the long diagonal will be:
CP: 31.35mm (1.23”)
SP: 28.96mm (1.14”)
EP: 24.71mm (0.97”)
GP: 21.35mm (0.84”)
PP: 20.26mm (0.80”) - If all your coins have a matching 20mm (0.79”) long diagonal, then their thicknesses will be:
CP: 3.90mm (.15”)
SP: 3.33mm (.13”)
EP: 2.42mm (.10”)
GP: 1.81mm (.07”)
PP: 1.63mm (.06”)
Data Used
Electrum Calculations:
Electrum is not a specific alloy – it is a name for any alloy of gold and silver. In order to obtain a coin, however, that is composed of those two metals, retains the same weight as either a SP or a GP, and achieves the PHB value of 0.5gp, it has to be a mix of 44.44‾% gold, 55.55‾% silver (by weight). That allowed the calculation of the alloy density of EP, and therefore the dimensions above.
Electrum is not a specific alloy – it is a name for any alloy of gold and silver. In order to obtain a coin, however, that is composed of those two metals, retains the same weight as either a SP or a GP, and achieves the PHB value of 0.5gp, it has to be a mix of 44.44‾% gold, 55.55‾% silver (by weight). That allowed the calculation of the alloy density of EP, and therefore the dimensions above.
Densities:
Cu: 8.96 g/cm3 | 4.72ozt/in3
Ag: 10.5 g/cm3 | 5.53ozt/in3
Electrum: 14.42 g/cm3 | 7.60ozt/in3
Au: 19.32 g/cm3 | 10.18ozt/in3
Pt: 21.45 g/cm3 | 11.30ozt/in3
Cu: 8.96 g/cm3 | 4.72ozt/in3
Ag: 10.5 g/cm3 | 5.53ozt/in3
Electrum: 14.42 g/cm3 | 7.60ozt/in3
Au: 19.32 g/cm3 | 10.18ozt/in3
Pt: 21.45 g/cm3 | 11.30ozt/in3
Total volumes of coins:
CP: 1.0136cm3 | 0.0619in3
SP: 0.8650cm3 | 0.0528in3
EP: 0.6298cm3 | 0.0384in3
GP: 0.4701cm3 | 0.0287in3
PP: 0.4234cm3 | 0.0258in3
CP: 1.0136cm3 | 0.0619in3
SP: 0.8650cm3 | 0.0528in3
EP: 0.6298cm3 | 0.0384in3
GP: 0.4701cm3 | 0.0287in3
PP: 0.4234cm3 | 0.0258in3
Fineness
All coins are calculated at 100% purity (1.000 fine). That is unrealistic, but it is not possible to account for the dozens of possible alloys and blends that one might justify using various historic models. These numbers should be good enough for pretty much anything your players want, but if you really want to get in to fine details or something, consider that debasing a coin will adjust its weight or its size. Lead is denser than copper or silver, so a coin of equal weight would have to be smaller. It’s a lot less dense than gold or platinum though, so the coin would have to be larger to make up for it. This is relevant, because coin scales of the time (used to weigh coins and ensure their value) also frequently had gauges to ensure the size was accurate as well. A warning to any tricksy rogue players who want to try their hand at counterfeiting. Also, the penalty for counterfeiting was usually death.
All coins are calculated at 100% purity (1.000 fine). That is unrealistic, but it is not possible to account for the dozens of possible alloys and blends that one might justify using various historic models. These numbers should be good enough for pretty much anything your players want, but if you really want to get in to fine details or something, consider that debasing a coin will adjust its weight or its size. Lead is denser than copper or silver, so a coin of equal weight would have to be smaller. It’s a lot less dense than gold or platinum though, so the coin would have to be larger to make up for it. This is relevant, because coin scales of the time (used to weigh coins and ensure their value) also frequently had gauges to ensure the size was accurate as well. A warning to any tricksy rogue players who want to try their hand at counterfeiting. Also, the penalty for counterfeiting was usually death.
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