Worldbuilding part 2: Coinage

This is part 2 of my not-quite-a-series-yet on worldbuilding, one of my favorite topics.  We discussed travel and time in part 1.  Got a worldbuilding topic you'd like to discuss?  Drop it in the comments!

Coinage

Money itself is a pretty deep subject and already assumes that civilizations in your world have such a concept.  We'll assume that's true and use coins as an example of the kinds of details that can really help your world come to life.  You don't need to solve for these things, but then again we don't really need to build our own worlds either, do we?

How Big Are US Coins?

I stated it in the first part:  verisimilitude is important to me.  So when I hear about characters in RPGs carrying around thousands of coins I have to ask stuff like "how do they carry all those coins?" and "how much does it all weigh?"  Gold is a stupidly heavy metal and really big coins are going to be really unwieldy in any kind of count over a couple digits.  To understand this better for my world, here's some of the work I did.

For those of you not in the US, I'm pretty sure you can do similar homework.  All I'ma say about that, is that Wikipedia is awfully well stocked.

• A penny is 0.75 inches in diameter (~19mm), 1.55mm thick, and weighs 2.5g.
• A nickel is 0.835 inches in diameter (~21mm), is 1.95mm thick, and weighs 5g.
• A quarter is 0.955 inches in diameter (~24mm), is 1.75mm thick, and weighs 5.67g.
• A half dollar is 1.205 inches in diameter (~31mm), is 2.15mm thick, and weighs 11.34g.

"So what?" I hear you thinking, unnamed anonymous reader.  "What does that even mean?"  

• $5 of pennies is heavier than most swords (no, really; swords aren't as heavy as you might think).  
• 100 nickels is well over a pound.
• $63 in quarters is heavier than the average longsword (these are two handed weapons--don't believe DnD's claims about this weapon!)
• 800 half dollars weighs just over 20 pounds, more than the weight of a historical chain hauberk!

But wait!  This is with modern materials, mainly zinc and copper which are relatively light.  Let's convert all these to silver and gold with the power of maths!

• Pennies are 97.5% zinc and 2.5% copper, (7.140 g/mL*97.5%+8.96 g/mL)
• Nickels are 75% copper and 25% nickel (8.96 g/mL*75%+8.9 g/mL)
• Quarters and half dollars are ~92% copper and and ~8% nickel (you get the idea)
• Silver is 10.5 g/mL
• Gold is 19.32 g/mL

Assuming I've wielded my arcane alchemy maths correctly and assuming non-alloys:

• 100 penny sized coins would weigh ~0.8 pounds if silver and ~1.5 pounds if gold
• 100 nickel sized coins would weigh ~1.3 pounds if silver and ~2.4 pounds if gold
• 100 quarter sized coins would weigh ~1.5 pounds if silver and ~2.7 pounds if gold
• 100 half dollar sized coins would weigh ~3 pounds if silver and ~5.4 pounds if gold

In real-world objects:

• a 12oz can of your favorite fizzy beverage would be around 35 nickel-sized gold coins.  
• A gallon of water would be about 568 quarter-sized silver pieces.  
• Your 10 pound bag of charcoal would be 185 half dollar sized gold coins.  
• A thing costing 15,000 gold pieces the size of a penny would require a pile of coins weighing as much as a reasonably sized anvil! 

It is just plain not practical to carry around that kind of weight on a regular basis.  Things shouldn't cost that much or at the very least, the top level coins should have more value.  In my world, a gold piece is a really valuable coin a few of which is enough to buy a horse or a house in some places.  Smaller denominations stay useful including the humble copper piece and as a result most folks aren't carrying around more than a half dozen coins.  I have a handy chart on my GM screen with sizes, weights, and counts per pound of each denomination across many nations including their names and nicknames which brings me to my next topic.  Let it never be said that I'm not a master of the smooth segue.

What Are Your Coins Called?

While copper, silver, and gold pieces are easy to remember and have a clear denomination, I think they're awfully boring.  We don't call pennies "zinc pieces" do we?  Nickels are the exception that proves the rule, I guess, and have their own fascinating history.  Do all of your world's nations share the same coins?  Real world nations don't!  So what do you call coins in your world?  

There's lots of places to take inspiration from.  The Romans had piles of different types of coins in their thousands of years of history and that's just one(ish) nation!  Many US coin names have interesting histories (though not quarters--sorry, bud).  Here are some examples from around the world.

Kallvor's coin names follow a theme on a per-nation basis.  Lanvelon's coins are largely named after Roman coins (Sestertius, Denarius, Solidus).  Few people would pick up on that and those that do can learn something about the nation that minted them by connotation (old empire, now a vestige of its former power concentrated in a single city).  Kezhor coin names follow practical military gear (armor) for a practical and militaristic nation (Shield, Helm, Cuirass).  Querthon owes its coin names from one of my all-time favorite games (Sword, Scepter, Crown).  Those crafty elves do name their coinage after the metals they're made of (Aerius, Argentius, Auereus, Melleus) which are cognate with their Latin names.  Two of these will ring true for fans of the periodic table (Ag and Au); the last one I made up.

Deserving of their own paragraph, the dwarves of Kallvor control most of the trade in the known world.  Named after their deity of trade and prosperity, Tharkur, the backbone of their currency (silver pieces) are known far and wide as Tharks and for gameplay's sake, sets the standard for currency realm-wide.  Thark is also the common dwarven name for trader or merchant.  The single smaller denomination is the Penz or Pawn in Common.  Gold pieces are known as Royals or Kings in common (etymology note:  the word royal comes through French from Latin so I'm OK with royal being the dwarven word here).  You don't often need more than a gold piece, but if you do, the dwarves have you covered with Archroyals or Arcs hearkening to their earlier days of Archkings presiding over multiple undermountain kingdoms.

OK, now the fun part!  We've established that the lowest dwarven denomination is the copper pawn (Penz).  This leads us to the all-too-familiar sayings, now dwarvenized to "here're my two pawns" and "I ain't got two penz to rub together".  Dwarves don't spit nails as much as they "throw Tharks" when they're angry and since ducks aren't often found in either undermountain kingdom, they tend to get their "Royals in a row" with the added connotation of a tradesdwarf rolling their coins after a successful day.  On top of being awesomely alliterative, it also gives the connotation of importance because language is awesome.

But Wait, There's More!

Coinage is really complicated!  Is the value of the coin the value of the metal that makes it?  What shapes are they?  Can you distinguish between different nations' coins at a glance or are they all boringly similar shapes and sizes?  We haven't even talked about exchange rates, minting, or metallurgy yet!  This, like all of the topics I'll cover in this not-quite-series-yet are deep rabbit holes that can add depth and character to your world.