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A Portable Hole (DMG I p.264) is described as being 6' in diameter and 10' deep, which translates to over 282 cubic feet or just over 8000 liters of empty space. But unlike the Bag of Holding (DMG I p.248) which has a weight limit, or the spell Hoard Gullet (Dragon Magic p.68) which has both a weight and volume limit, the Portable Hole is merely limited by its volume.

So how do I know when a Portable Hole is full? Do I have to calculate the volume of each item before putting it in there (and disregarding how to optimally use the space I've got)? Or is there a weight limit somewhere that I missed? Or is this just not mentioned in the rules? I'd rather not haul around a full bathtub for measuring purposes, you see.

Thomas Jacobs
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There are no limits. The portable hole is simply massive. Once you have one, you're supposed to be well beyond the point where tracking storage space has any meaning, and the lack of specific rules is supposed to indicate that you just don't worry about it. It's huge. There's enough room. You're a high level adventurer; don't you have more important things to be worrying about?

KRyan
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Although I'm inclined to agree with KRyan, if you do want a more hard-and-fast rule of thumb...

A litre of water weighs roughly 1kg. Multiply that by 8000 and you've got, well, 8000kg of space. Obviously, you're probably going to be using that space to store precious metals like gold (treasure) or steel (weapons), so using the density of gold...

gold is very dense: a cubic meter has a mass of 19,300 kg. By comparison, the density of lead is 11,340 kg/m3.

If my math is right, 282 cubic feet is around 85 cubic meters, so a portable hole filled with gold would be 1,640,500 kg.

What if you want to store something other than gold? Well, the same Wikipedia page states that the densest element (osmium) is around 22 kg/m3. Gold's a good benchmark for the heaviest stuff an adventurer might store in a portable hole.

So yeah, you can pretty much throw the whole weight thing out the window at that point.

EDIT: So, it looks like there is some confusion as to my rationale for the calculations that I did. My original thought upon seeing the question was, "Is there a way to find out how much a solid mass of the dimensions of a portable hole weighs? If so, then you can use that to gauge how much stuff fits in the hole, because D&D items have weight/encumbrance." Unfortunately, different materials have different weights/densities, so I tried to calculate the upper limit that you might see if the hole was full of the heaviest stuff an adventurer might carry; specifically, gold. That way, it would be possible to illustrate that the amount/weight that would fit in the hole was so massive that it was really a non-issue. In other words, any specific thing that weighed enough to take up a decent chunk of the available weight (like a dragon or an elephant) would also probably be so large that it wouldn't fit in the dimensions of the hole, and anything smaller (like coins or other treasure) would take up so little volume that you'd be able to carry as much as any adventurer would be likely to ever have.

Sandalfoot
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  • D&D 3.5 weight units are... well, they're definitely not kilograms. They're not even really pounds, even though they get called that, they're kind of a fudge value that's supposed to encompass both weight and how cumbersome an object is. So I don't think real-world values are going to help much. – KRyan Jan 16 '15 at 20:40
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    I agree. I haven't played D&D since all of the weights were in "coins". I don't even want to imagine how many coins' worth of encumbrance you could fit into a portable hole... but I totally want to play in the game where that becomes an issue. Talk about first world adventuring problems! – Sandalfoot Jan 16 '15 at 20:44
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    To clarify: I used real-world numbers to illustrate that the weight limit is so massive that you should just really hand-wave it. – Sandalfoot Jan 16 '15 at 20:47
  • This answer is admittedly much more precise than "one million orcograms", though not nearly as satisfying as measuring everything in orcograms. – BrianH Jan 16 '15 at 21:55
  • Thing is, if you go by mass instead of weight 282,743 cubic feet of gold equals 155.000 kilograms, which is 341.716,5 pounds. If these are imperial pounds and you use the rules that 50 gold coins are 1 pound, you are looking at a total of, rounded down, 17.085.825 gold, 31 silver and 93 copper. Your 1.6 million kg on the other hand is by the same calculation equal to 180.834.170 gold, 55 silver and 71 copper. Big difference there. – Thomas Jacobs Jan 16 '15 at 22:27
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    I think you're focusing a bit too much on the "coins" aspect of it, Thomas. Players are going to store more than just raw coinage in a portable hole. You could have stopped at "341,000 pounds" and come to the conclusion that only in very rare circumstances would an adventurer ever have the need to cart that much stuff around. – Sandalfoot Jan 16 '15 at 23:03
  • Coins aren't solid metal unless you have some very strange square coins. The best packing you're going to get is about 2/3 metal with round coins. – Loren Pechtel Jan 17 '15 at 04:27
  • @LorenPechtel: I was just about to make the same observation, though I'm not quite so optimistic -- I was going to say 60%. Carefully-stacked coins can fill about 90% of the container, but random packings are usually much worse. If you have hard numbers for these I'd be very interested! – Charles Jan 20 '15 at 16:57
  • @Charles I seem to have mistaken sphere packing for coin packing. You're right. – Loren Pechtel Jan 20 '15 at 18:28
  • @LorenPechtel: I think it's a fascinating question, and it led me to the thesis of Wenli Zhang who considers random packings of cylinders. Unfortunately the smallest aspect ratio he considers is 1, and we want more like 0.08. So I don't know the answer, although it's less than 65% if the distribution is unimodal (as the author hints). – Charles Jan 20 '15 at 18:38
  • kg is not a measure of volume. – Davo Jan 25 '19 at 13:25
  • @Davo While you're correct, in this case it's being used figuratively to illustrate how the maximum volume a hole can hold can be used to calculate the maximum weight of the hole's contents. – GMJoe May 02 '23 at 22:36
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Correction to Sandalfoot’s calculations, the adjustment from cu.ft. to meters results in a volume of 7.985 m^3 [282 ft^3 * (0.3048 m/ft)^3]. For rough estimate divide his maximum mass by 10, if you’re a stickler for mathematical consistency multiply masses by 0.0939.

Given that, 7.985 m^3 is not a particularly massive amount of space (could fit 3 couches/sofas completely inside). I would say if you want to be consistent to RAW and be precise use the volume of a known object, like a couch/sofa (~2.5m^3), to estimate the volume of any large objects the party may attempt to put into the hole(I would recommend considering most smaller objects to be negligible in volume until such a point where the party starts hoarding everything small item they loot or find at which point use an estimate of say 1-2m^3 for every 100 small items).

Alternatively if you don’t want to bother with this you could home brew to create a rarer portable hole with increased volume to a point where it is ultimately irrelevant, could even serve as a portable keep with rooms for the players to store stuff and sleep— as long as the hole is open of course ;).

DMAsymptote
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While by the game mechanics provided, a portable hole has no strict limit to what can be put in it beyond the physical size, for my own campaigns I've put a practical limit using the density of water as the "average" for what they can put in it, which is ~8 lbs per gallon, and 1 cubic foot is roughly 7.5 gallons. 282 cubic feet roughly translates to 2110 gallons, and 2110*8 = 16880 lbs. Naturally, various random objects strewn about inside the hole will cause some empty space to exist, so I round down to a nice even 16,000 lbs.

Now, if the players decide they are going to store ONLY gold, silver, etc in the hole, I'll allow them to store more, but my players have always decided to throw everything, including the kitchen sink into it so the 16,000 lbs limit works as a nice rule of thumb.

Adam
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While in general I agree with KRyan I wouldn't make it entirely limitless--while I would never bother to track small stuff in a portable hole big objects are another matter. A 10' ladder fits in the hole--but woe to anyone who tries to put it in or take it out while in a dungeon unless the contents are carefully boxed up. If you have 50 million cp loose in that hole it's going to take you ages to free the ladder from it.

I would be even stricter about an 11' ladder--it fits but only at an angle. The 12' canoe isn't going in at all.

Loren Pechtel
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    A 10' ladder fits into a portable hole. This is proven by the fact that almost every portable hole contains a 10' ladder, placed there by the owner in order to facilitate easy item retrieval. – GMJoe Jan 19 '15 at 02:40
  • Sure, but I'm talking about pulling the ladder out to use it for something other than accessing the hole. – Loren Pechtel Jan 19 '15 at 03:35