D&D 5E Coins and weights in D&D - the math doesn't add up!

[Elderbrain]

I have looked thru all the D&D PHs and DMGs I could find (2nd Edition, Third, Fourth, and Fifth) and they
all say it's 50 coins to a pound (any type coin - copper, silver, gold, etc.). However, they ALSO claim each individual coin weights about a third of an ounce, which means three coins for every ounce, correct. Now, a pound contains 12 ounces, doesn't it? So 3x12=36 coins to a pound - but the books says 50! Is this a math error perpetuated for multiple editions without being caught and corrected, or am I making a mistake somewhere...?

 

[Tony Vargas]

A pound contains 16 oz, so 1/3rd of an oz per coin comes out to 48 per lb. Close enough.


Edit: Besides, in 'real' D&D (1e AD&D), coins were 10 to the lb, not 50. Fantasy coins are big, dammit. You never see a dragon lounging on a pile of dimes and krugerrands.

 

[GSHamster]

It's a little complicated because there's a system called "troy weight" which is used for precious metals and gems. There are 12 troy ounces in 1 troy pound. The more common system, called avoirdupois, has 16 ounces to 1 pound. However, the troy ounce is a bit heavier than the avoirdupois ounce.

See https://en.wikipedia.org/wiki/Troy_weight

For the purposes of D&D, I think everything uses the avoirdupois system, so 16 D&D ounces = 1 D&D pound.

 

[Umbran]

A pound contains 16 oz....

Typically, yes. When all of the weights are given in terms of pounds, you should be thinking of the modern pound, which is equal to 0.454 kg, and is divided into 16 ounces.

However, because history is complicated, we can get pedantic. Many measures of mass have been called a "pound". If you are speaking strictly of precious metals, you may see reference to the Troy pound, which is divided into 12 Troy ounces. A Troy pound is about 0.82 standard pounds, or 0.373 kg.

That's probably where he got the 12 ounces from. It would not be appropriate to cross measures there- assume the gold weights given are *standard* pounds, not Troy pounds.

 

[MG.0]

If you really go back (1st edition, or Basic D&D) you'll also find that the weights were never really meant to literally be the wieght of things. It's a combination measure of the weight and bulkyness of an object (encumbrance) given a simple numerical weight for ease of computation. I'm not sure how much bulkyness factors into the weights given in the 5th edition PHB, but it used to be common to see light but large items to be given a higher weight than you would expect.

If you go way back past the 10 coins per pound of first editon, you find origianlly D&D measured weights in coins = CN. No real world units were used. I actually think that might be better as it keeps things abstract and prevents people from trying to establish real world weights for everything.

 

[EzekielRaiden]

Incidentally, if you work from the other direction, that is if you start with "a pound of coins" and work backward to "the weight of one coin," things fit even more nicely.

1 lb/50 coins = 16 oz/50 coins = (16/50) oz/coin = 0.32 oz/coin, or just one seventy-fifth (0.01333...) of an ounce off from the expected value.

0.32/(1/3) = 0.32*3 = 0.96, meaning each coin weighs 4% less than a third of an ounce. Accuracy to within 5% of the expected value is quite good, particularly for a quasi-medieval society where currency debasement is probably rampant.

I'll also echo what the others have said. This is pure avoirdupois, and has nothing to do with the Troy system. Another way of putting it is that each coin should weigh 140 grains, and there are 7000 grains per pound (both avoirdupois).

 

[Hriston]

If you really go back (1st edition, or Basic D&D) you'll also find that the weights were never really meant to literally be the wieght of things. It's a combination measure of the weight and bulkyness of an object (encumbrance) given a simple numerical weight for ease of computation. I'm not sure how much bulkyness factors into the weights given in the 5th edition PHB, but it used to be common to see light but large items to be given a higher weight than you would expect.

I always thought 25 lbs was a bit much for a two-handed sword.

 

[Jester David]

...
Oh man, I hate imperial. I'm glad I don't actually know the specifics so I can just assume it all makes sense and not worry about it. The above all sounds super confusing.

 

[CapnZapp]

I wonder if I'll see the day when the Americans start using metric...

 

[delericho]

A pound contains 16 oz, so 1/3rd of an oz per coin comes out to 48 per lb. Close enough.

This.

Incidentally, UK £1 coins are 46 to the pound, which is a very useful fact when running games here.