Gems 10gp

agate    azurite.   Quarts (blue)   hematite. Lapis lazui    malachite.  Indian

Gems 50 gp 

bloodstone.  Moonstone.  Onyx.   Amber     amethyst.  Jade   pearl (white) 

gems 500gp 

garnet.  Black pearl.  Topaz (gold \yellow)

Gems 1000gp

EMERALD         opel.    Sapphire.    Ruby   

gems. 5000gp

emerald (clear)   diamond. 

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SIZE.        WEIGHT.             × BASE VALUE 

6'dia.        14 ibs.                 50000gp

3'dia.        2 ibs.                   5000gp

2'dia.       ½ ibs.                   1000gp

1'dia.       0.064 ibs.            100gp

½'dia.     0.008. Ibs.            20gp

¼' dia     0.001 ibs.             BASE VALUE

⅛'dia.     0.000125 ibs.      BASE VALUE \10

This is my opinion if you have any questions please contact me

ENJOY!!

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Indian was a mistake sorry

 okay thanks i only  did this for weight value

Hi there, I just did something similar for coins (I can share later if you're interested) 

How did you get the diameter/weights of your gems?

I wasn't sure I completely agreed with your gemstone sizes, I so I did wrote my own version, this is the result...

I listen to various D&D podcasts, and the one thing that has always bugged me is a character's ability to reach into their pockets and pay for an item that costs thousands of gold pieces. This got me thinking, even if someone paid for high end items in Platinum, that would still be many lbs worth of coins. So I wondered what other precious metals coins might be minted from in D&D.

The Player's Handbook states that 50 coins weigh 1lb making 1 coin approximately 1/3oz. To be exact, one coin weighs 0.32oz.

I found a webpage detailing the values per pound (lb) of each metal in D&D. While I already knew the 4 basic coin metals, I was interested to learn that Mithral was worth 5X more than Platinum, and Adamanatine was worth 10X more than Platinum. These two metals would make great high value coins, with the Mithral coin probably less common in circulation (similar to the Electrum coin). The addition of Adamanatine would automatically bring a 5,000GP item (100lb of coins) or 500PP (10lb of coins) item down to just 50AP (1lb of coins). I also noted that certain territories minted special coins that were really only usable within their borders (looking at you Waterdeep) for simplicity I have omitted these coins.

Then I got to thinking about currency in general and what the actual size of a coin might be. Thanks to the webpages I found, I not only had the values of the metals, but also their density in lbs/ft3.

Now while I do find pounds, ounces, feet, and inches easier to visualise. I feel they become unwieldy for smaller measurements. After some research I found that ounces can be split down further into drams and grains, but this is not easy to calculate on a machine programmed to work in base 10.
Similarly fractions of an inch are just as awkward when you get down to 47/64ths etc. For this reason I decided to convert my results to the metric system.

I found a calculator online that allowed me to take the density for these metals and solve the volume of a given mass. From there I was able to reverse calculate the volume of each coin. The coins depicted in the Player’s Handbook are, I believe, specific to Waterdeep. Again, understanding that different territories will use different shapes for coins, I cannot possibly account for every coin shape a player may encounter. For this reason, and the sake of simplicity, I am assuming all coins are round and roughly 1.5-3mm thick.

Having figured out coinage, I remembered that Gems are also used as a form of currency. While there are defined values for Gems in the books, there is no mention of weight. Some research turned up some interesting results from earlier editions but it still didn't satisfy my curiosity.

So I researched the density (or specific gravity) of the various Gems. The results were given in g/cm3.

Then I had to decide what shape each gem would be. For simplicity (and with the exception of pearls which are spheroid) I categorized gems into 2 shapes, Cabochon (opaque stones) and Round Cut (transparent stones), and then determined size in mm based on the carat weights of each stone. I found a very handy gem weight calculator online that did all of the hard math for me 😊.

For visualisation purposes, Cabochons are generally pebble shaped, flat on the base with a domed surface, I have generalised thicknesses for each size category and assumed that stones are circular, or very close to circular.

Round cut stones are synonymous with diamonds, and gems in general (usually used to portray gems in cartoons etc) which is why I picked this particular cut. I have tried to keep the measurements as symmetrical as possible.

For all three types (cabochon, round cut, and spheroid) measurements are written as Length X Width X Depth of the stone in mm.

Now, back to D&D. In 5e, gemstones are listed with values, but no information as to size. Browsing the Internet, I discovered that the most comprehensive information regarding gemstones in D&D was published in the AD&D 1e DMG, with further refinements published in Dragon Magazine issue 8.

The tables published were still not exactly easy to read as they listed type or size against the same value of gem with a footnote stating that larger low value gems wold be worth the same as smaller high value gems.

There were originally 6 tiers of stone value...
10gp Ornamental / Very Small
50gp Semi-Precious / Small
100gp Fancy / Average
500gp Fancy (Precious) / Large
1,000gp Gem / Very Large
5,000gp Gem (Jewel) / Huge

 For my tables, I removed the size from the value table as it makes things confusing. Instead the values listed in the table will represent an average sized stone of each tier. With a sliding Value-per-Carat scale based on stone actual size.
Additionally I have pegged the weight of an "average" sized stone as 1 carat, and adapted the size values round that which allowed me to add one more size category (gigantic)...

So we will have a table of stone size/type with cost per carat listed in the grid denoting rarity.

Finally I have included a spell components table to visualise those also – note that where a stone is required to be in powdered form, or multiple stones are required to meet the designated value, I have used the lowest cost per carat as no-one in their right mind would grind up a more expensive (larger) stone unless absolutely necessary.

Holy crap, I don't even play Fifth Edition and this is fantastic. I'm gonna put this in Silver standard and use it in my games. Thanks a lot!

Excellent work! Really detailed and extremely useful for stuff like bags of holding, carrying capacity, and exploration.

Edit: Inaccuracy.

This is really cool! I think the Gems might need to be divided by 10 to make them align better with material component costs, but this is all and all fantastic work!

Some notes from the peanut gallery
1) until the US went off the gold standard in the 1930’s coins actually contained their value in silver and gold. This was true all the way back Croesus and the first coins the coin’s value was based on the metal content. Inflation/devaluation occurred when the coins were adulterated with base metals to inflate the number of coins in circulation. Coins were often cut down to make change when smaller coins were unavailable. This is the origin of the term “ piece of eight” for the Spanish silver real. It was frequently cut into 1/8ths that were known as “bits” ( hence the old chant : 2 bits, 4 bits, 6 bits, a dollar”) each worth about 12 cents.
2) while the work done was remarkable and detailed and some folks will find it useful the old AD&D DMG tables are probably all most of us actually need - but you have to understand them to use them properly - it’s really 2 separate tables squeezed together - a “value” chart and a “size” chart the value chart runs from ornamental tp precious and gives the base value of these types of gems - for a very small sample. The “size” chart shows how the size increases the value from that base. Keeping in mind that a huge ornamental stone might be as large as a throne while a huge diamond might not be as large as a fist. For most game uses that should be all most of us will need. Of course, the reality of gemstone pricing sin the real world gets incredibly tricky as factors like depth of color, clarity, hardness, refractive index, style of cut, source region, etc can have major impacts on value.

This is wonderful, and the data hound in me loves every bit of it. As a DM, I see that the majority of your spell components are 0.007oz or less. Taken as the mode, 1 pound is approximately 2000 (~2285) gems. So, for simplicity’s sake, we could just say 2000 gems/lb. Probably insignificant unless you run into a dragon’s hoard. Super cool!

A gram is .0022 of a pound 2.2 lbs/kg /1000g/kg) rounding its 2/1000th. The density of gemstones ranges from @2 gym/cm3 to @ 4 gm/cm3  with a cm3 being roughly the size of the nail tip of your little finger. So yes the weight of even large gemstones is generally minimal. Most ornamental gems are actually varieties of quartz with a density of 2.7 gm/cm3 so you have to have fairly large pieces to have substantial weight. For reference the largest diamond ever found (the cull in an) weighed 621.2 grams ( over 3000 carats) or a bit over 1 pound uncut. The largest Ruby is only @ 55 carats. Most of your huge ( precious) stones are going to be varieties of beryl where individual crystals can weigh upto tons. In many cases the beryl crystals are multicolored and clear throughout, large corundum crystals ( Ruby and sapphire) are mostly “waste” rock with only small areas of colored gem quality material ( the rest can be crushed for abrasive (emery). The largest crystal I’ve actually seen was a beryl crystal roughly 3 feet across by 18” high clear throughout out and sections of 5 different colors - in the back rooms of the American Museum of Natural history.