So, a few sessions back, my DM allowed us to fill our Portable Hole completely with gold coins and various other valuable trinkets and loot from a treasure room we discovered. We have yet to set out and count all of the gold and discover each trinket, bobble, or other piece of loot, but I believe it is safe to say that you can comfortably ignore the small amount of items that are not gold coins and still receive a fairly accurate approximation, as the DM stated that it is mostly consisting of gold coins.
Here is my math:
A Portable Hole is a 6' diameter hole, and it stretches 10' down.
To figure out the volume (or how much gold can be held in the hole), the formula is Volume = π * radius squared * height. π = 3.14 and the radius is half of the hole's diameter (which is 6'), so the radius is 3', and the height is 10'.
-So the formula would be: 3.14 * 9 * 10 = 282.6 cubic feet available to fill inside the hole.
A cubic ft of Gold is 1,206 lbs. Now, obviously this is a solid, dense block of gold, but this is just an approximation of gold coins.
With there being 282.6 cubic feet available in the hole, that equals out to 282.6 * 1,206 = 340815.6 lbs of gold.
Since the PHB states that there is 50 GP to each lb of GP, that will become: 340815.6 * 50 = 17,040,780 gold pieces.
I ran this math by the DM, and he says that this checks out by his calculations, give or take a small percentage being non-gp items, and also accounting for the spaciousness of gp as opposed to the solid mass of a gold block, we could even say that this is anywhere from 10 - 15 million gp, which is still a huge amount of gold. Also, non-gp trinkets and items may even be worth more than the gold.
If anyone can help me find a more accurate means of determining the amount of GP, I would love to hear from you, as I conveyed my concerns to my DM that this is far too much gold for five 6th level characters, and he continues to say that we'll just be rich from now on, and has stated to me that there is no trickery about the gold and that it really is just that much GP.
I'm quite concerned that this may impact our game very negatively. Personally, my character shuns gold and does not possess a value over treasure, but there are several members of our group who are completely driven by it. I'm scared what could possibly be done with this much gold, as I am fairly new to D&D and I don't quite know what is available to those with heavy coin purses.