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Preface:

I am not tagging this for a specific edition, because the subject is very narrow. I believe it has not changed much through the editions. If the reviewers find that an edition is required, I'll add one.

Background

Given the medieval / renaissance technology, I am inclined to believe that the fineness of gold would be around 18 to 22 Karats. ref1 and ref2

There is the "magic" argument, and pure gold could be created by wizards. However, all settings have gold coins (even Dark Sun), and not many of them have enough mages to make this commonplace. Maybe only Netheril, who knows.

Question

What is the fineness of gold coins in D&D? Has it been discussed, or disclosed, in any official source material?

user17995
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Mindwin Remember Monica
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    Why can't gold have different fineness in different game worlds or settings? – enkryptor Oct 02 '17 at 15:42
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    I'm inclined to think this is a bit broad too -- what problem are you trying to solve in asking this? You're asking for every setting and every edition, and though it may only be defined in some, that just means it's more likely to just be in a setting and edition you're not using -- what has that be useful to you? – doppelgreener Oct 02 '17 at 15:55
  • If you narrow editions, I can give you something of an estimate. It can't be an exact answer, because...naturally....D&D doesn't go into such fine details as the metallurgic composition of currency. – guildsbounty Oct 02 '17 at 15:57
  • Actually, scratch that...I can give you an estimate across the board. – guildsbounty Oct 02 '17 at 15:59
  • @enkryptor it should. I wouldn't expect Athasian gold coins to be as pure as Birthright or Oearthian coins. – Mindwin Remember Monica Oct 02 '17 at 16:44
  • @doppelgreener I'm not asking for "every". I'm asking for references on source material, without restricting it to one line of products. While it may be broad (and I open my post with that acknowledgement), I don't feel like it falls into "There are either too many possible answers, or good answers would be too long for this format. ". Is this a hard to answer question? yes. If the subject was addressed in some rare book, is there a chance someone would remember it? I guess they would. (tbc..) – Mindwin Remember Monica Oct 02 '17 at 16:55
  • @doplegreener (continued...) Back to the quote, there are not too many possible answers, and an answer would not be too long for a stack post. But this is not an easy question, and not all the questions should be easily answerable. But IF this question gets an answer, it would be a rare one. Making the broadest knowledge base on the subject sometimes requires going into those hard to reach places. My bet is this page is one of them. – Mindwin Remember Monica Oct 02 '17 at 16:57
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    @Mindwin Given answers are expected to be reasonably comprehensive, you are asking for "every" by not otherwise limiting it down. I could revise that from "too broad" to "unclear", in that you're not saying what problem you're solving because frankly this is bizarre in scope. You've acknowledged you would expect it to vary between settings, for instance. – doppelgreener Oct 02 '17 at 16:57
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    @dopplegreener Now that i read your recent comment, I take maybe it is a X Y problem in disguise. I can admit that. I'll work on it. Can you close as unclear for the moment? – Mindwin Remember Monica Oct 02 '17 at 16:57
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    It does look like an XY problem, yes. We would ask at times like this: what problem are you trying to solve? We do prefer people be specific to their own issues, rather than artificially broaden their solution to potentially help others, so a desire to create a broad knowledge base is a laudable goal but not what we look for in questions -- ironically being a bit selfish is the best way to be helpful to the most people, since trying to make questions broader tends to backfire in making them less helpful to any specific person. (Closed as unclear, per your request.) – doppelgreener Oct 02 '17 at 16:59
  • @doppelgreener I know. It just had not struck me until now. Maybe tonight I'll work on it. – Mindwin Remember Monica Oct 02 '17 at 17:01
  • @Mindwin At whatever pace you're comfortable -- [chat] will also be happily available to assist. Sorry if I was going a bit overboard on it in that last comment. – doppelgreener Oct 02 '17 at 17:57
  • Edited for format and organization, I don't think I improved the question very much. – KorvinStarmast Oct 02 '17 at 19:43
  • Perhaps you could narrow your question to a specific setting and ask whether the face-value of their gold coins is fiat? E.g.: for a while back in 2005, the metallurgical value of the 5¢ coin exceeded that of the face value — which is tied to the USD, which is valued by fiat; prompting legislation by the US Mint to forbid such actions: https://www.usmint.gov/news/press-releases/20061214-united-states-mint-moves-to-limit-exportation-melting-of-coins Anyways… Such is an example of something which could be pertinent to your group, albeit of more interest to numismaniacs or economists. – can-ned_food Oct 02 '17 at 20:27
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    The main reason I think edition matters is that gold coins were 10 to the pound in earlier editions and then 50 to the pound later. – mxyzplk Oct 03 '17 at 01:26
  • I'm not sure this is really an answerable question within the rules (other than, uh, D&D designers usually don't go into this kind of thing), but I love the nerdy "answer it anyway!" answer. – mattdm Oct 03 '17 at 14:29
  • I don't believe this question is answerable. First, gold as used by players is heavily devalued already. This is reflected in the "sell items for half price" trope; essentially the entire rest of the world is gauging adventurers outrageously, and one reason for that is likely that the coins they use have wildly varying values. Second, I see no evidence that fineness is standard across different nations within the same setting. Even if e.g. Waterdavian fineness is tightly regulated and all Thayan coinage is pure from conjury, that implies nothing about Menzobarrenzan currency. – fectin Oct 04 '17 at 13:11
  • I vote to change the closing reason to "Too broad" (I think I remember that in ONE supplement there was a notion that coins from one city were worth more than from another due to fineness, but there are HUNDREDS of supplements and this is not specified to one such block of supplements, making it too broad, let alone the edition problem) or "opinion based" (as each GM might decide to handle the fineness question differently. Maybe even "Off Topic", because this is to some degree a RL research question. – Trish Oct 08 '17 at 12:47
  • @Trish its fine, let sleeping dragons lie. – Mindwin Remember Monica Oct 08 '17 at 12:48

1 Answers1

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As the rulebooks do not give an actual answer to this, the best I can give you is an approximation.

What we know:

Throughout D&D rules across editions, a gold coin has most frequently been described as being about the same size as a US Half Dollar Coin. This citation comes from either a verbal description ('about an inch across.' ref: p212 of 4E PHB), or from an 'exact size' picture (ref: p168 on 3.5E PHB). So, for simplicity's sake, I am going to use the thickness of a half-dollar coin (is thick enough to be sturdy) and the 'inch across' quotation and image.

A quick check on Wikipedia tells me that a Half Dollar Coin is 0.085 inches thick. This gives us a volume of 0.067 cubic inches.

Given that pure gold weighs 0.7lbs per cubic inch, we can compute that a half-dollar sized coin should weigh 0.0469 lbs.

In Basic D&D and AD&D 1E, a gold coin was described as weighing a tenth of a pound. Which is...frankly...too heavy. The coin would have to be nearly twice as thick in order to give you that much heft.

However, from AD&D 2E onward, the weight of a gold coin has consistently been held to be one third of an ounce, or 0.0208lbs. (ref: 5E PHB p143, 4E PHB p212, 3.5E PHB p112). Thus, we could reasonably assume that either the coins are smaller than advertised, or they are not pure gold.

Historically, copper has been used as a common material to alloy gold with for making coinage. Copper weighs 0.324lbs per cubic inch, which would give us a pure copper coin weighing 0.0217 lbs....which is still too heavy. So it can't be a copper alloy. Tin is another option, and it weighs 0.204 lbs per cubic inch. A pure tin coin of this size would give us a mass of 0.0137 lbs. Tin is the lightest material that gold is commonly alloyed with that would be available in the middle ages, so we can guess that the gold is alloyed with tin.

So, to compute this, we have two equations as a system...given that x is the percentage of gold and y is the percentage of tin.

$$x + y =1$$

Representing that the percentages must add up to 100%

$$x*0.0469 + y*0.0137 = 0.0208$$

Representing that the percent of gold and tin must add up to 1/3 of an ounce.

Solving this system of equations gives us the following values

$$x = .2139$$ $$y = .7861$$

Which translates to a coin that is 21.39% gold and 78.61% tin.

This translates to 5K Gold...a quite low gold content. With a gold/tin mix, I'm not sure this would even still look like gold. If the coin were smaller, thinner, or heavier...it could have a higher gold content but, as described in the PHBs...5K is the highest fineness I can mathematically produce..

Note

There's a complication to this worth mentioning. According to 5E PHB p157 and 3.5E PHB p112: 1lb of gold is worth 50gp. And weighing a third of an ounce, 50 gold pieces equals one pound. This equality seems to exact to be a coincidence...that a pound of gold coins is equal in worth to a pound of gold? While not any form of concrete evidence...it does raise a secondary possibility:

It is distinctly possible that the coins are, in fact, 'pure gold,' and the mismatch in weight and/or size is simply because the designers didn't bother with the math, and set the weight based on a gameplay decision rather than on realism. Simply saying "this seems like a good weight for a coin, in terms of how much weight an adventurer can carry...and we want our coins to be pretty large in size...so make them about the size of a half-dollar."

And if you're concerned about difficulty....D&D is set in a society that has reliable and sturdy steel production. Refining 'pure gold' is easier, and was accomplished far earlier in history.

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guildsbounty
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    I have no idea. My rig went offline for a few minutes while I was typing the answer...but otherwise....I guess I'm magic? (Or I just discovered a bug in the stack software...which would be weird.) – guildsbounty Oct 02 '17 at 17:33
  • I checked my timings, it appears that the question was closed while I was without a network connection. Bug report submitted on the core stack exchange meta. – guildsbounty Oct 02 '17 at 17:44
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    There's a small leniency window after a question's closed in which clients are still allowed to post an answer, if they somehow didn't get the memo that the question had been closed. – doppelgreener Oct 02 '17 at 17:58
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    coins were worth more than the metal they were printed on from the time of the invention of coinage in ancient Mesopotamia through the fall of Rome. After the fall of Rome, Roman currency continued to be used for pricing all across Europe, even long after all the actual Roman currency was locked up in rich people's vaults. People would list prices in silver denarii and bronze asses, but would actually sell/trade goods either for other goods with commonly agreed upon values (like D&D's trade goods, but for different goods) or for newer, often locally-minted currencies like the pfennig. – Please stop being evil Oct 02 '17 at 21:27
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    In PHB 3.5 the coin image has a shadow. I wonder if anyone can calculate its thickness from the shape of that shadow. – Ols Oct 02 '17 at 22:13
  • @thedarkwanderer Thank you! Somehow that escaped me when I was looking stuff up. Updated answer for more correctness. – guildsbounty Oct 03 '17 at 16:40
  • On the other hand, coins were (at least in cologne) the following way: Input one MARK (that's 234g or 8 ounces) of gold, that's nominally 66 Gulden. A Mark of silver should be worth 256 Pfennig of coins... BUT the mint would melt in something like 1/9th of copper to make the coins harder, and then mint actually 74 Gulden/288 Pfennige, keeping the additional 8 Gulden/32 Pfennig for the treasury. – Trish Oct 08 '17 at 13:24
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    Highly porous foamed gold would account for this low weight by volume. If heated &\or pressed, the outside could still appear smooth. Notch-cut designs, punched holes (big square holes seem quite common?), & very deep engravings, could also subtract from the perceived density. I feel this is worth noting. – ProphetZarquon Feb 25 '21 at 08:48