# Why is the capacity of a barrel/bucket different for solids vs. liquids?

The PHB states the following volumes on page 153:

• Barrel: 40 gallons liquid, 4 cubic feet solid.
• Bucket: 3 gallons liquid, 0.5 cubic feet solid.

Why is the volume for solids lower than that for liquids?

• Barrel: 40 gallons liquid ≈ 5.3 cubic feet solid (holds less solid)
• Bucket: 3 gallons liquid ≈ 0.4 cubic feet solid (holds more solid)

Could it that they are trying to estimate packaging losses in the case of the barrel?

A bucket could be filled past the rim when you put a heap on top of it. I could imagine this is why the bucket takes more solid.

Propably not very important, but it made me wonder.

• I know of at least 3 units called "gallon" so please specify which one you are using for your calculations and why this particular one. Oct 19, 2022 at 11:08
• I'm from a metric part of the world, the whole non-metric volume system is quite alien to me. Given that D&D is a US-game, I wager these are US gallons/US cubic inches? Oct 19, 2022 at 11:15
• Sensible assumption, but on the other hand world building is based on medieval Europe, and we used to have quite a lot of feet and gallons. That's why I believe stating assumptions matter. Oct 19, 2022 at 11:19
• @Mołot I dont think OP can tell you exactly which gallon since the PHB doesnt say. Oct 19, 2022 at 12:07

## A liquid has no definite shape and assumes the shape of whatever container it is, solids have their own shape

Because of this when you fill a barrel (or any container for that matter) with a liquid, it will perfectly utilise all available space without any losses. When filling the same container with solids, there will not only be empty spaces between the items and the walls of the container but also between the items themselves, this way you're losing some of the theoretical capacity. Imagine a barrel filled with potatoes, they will not perfectly fit against each other, some space will be wasted in the barrel. I believe this is the reason for the differences in capacity, they are taking into account that packing solids will be more wasteful than liquids. Exactly how much space you waste depends on what sort of solid you're filling the bucket with (e.g. potatoes will be more wasteful than grains of sand) but you will never get the sort of perfect fit that you can achieve with a liquid.

As to the difference in case of the bucket, it could indeed be due to the fact that you can fill it with a heap on top if you put something solid in, which you cannot do with a liquid but I think that this is more for convenience, 3 gallons (imperial) is about 0.48 cubic feet, this is very close to 0.5, which is easier to work with than, say 0.4 and unlikely to make a difference in the context of a game.

The volume lost in case of the barrel is around 25%, which is consistent with the densest sphere packing in 3 dimensions, the math behind this can be found here for those who are interested: https://mathworld.wolfram.com/SpherePacking.html. This does assume that you're using items spherical or close to spherical in shape but I think this is a fair generalisation given that D&D is a game, not a physics simulator.

• Maybe, but apart from an explanation from the authors, this seems largely speculative. However, if you could cite a real world example showing similar ratios, I think that would be valuable evidence toward demonstrating that the authors were attempting to simulate real world differences. Oct 19, 2022 at 12:05
• @ThomasMarkov well, anything apart from the explanation from the authors is going to be speculative, they are the only ones that know why they did something the way they did and I don't think there's one available anywhere. The volume lost is around 25% which is consistent with the maths behind sphere packing Oct 19, 2022 at 12:17
• Design intent questions were originally banned because users could not resist providing speculative answers to them. We aren't looking for speculative answers, generally speaking. However, the note about sphere packing is a very good one, and observing that the ratios given are consistent with real math facts is not speculation, so I'm reversing my downvote for that reason. Oct 19, 2022 at 12:21
• I think it's just trying to give even numbers as a guide. The packing ratio I don't think makes sense because it's not the same in all cases and you wouldn't just say you can fit 4 cubic feet of poles in a barrel if they are twice as long as a barrel, or you could fit 8 cubic feet of poles. If the player or the gm are getting out calculators and arguing about packing density, they're doing it wrong. The guide just gives an estimate Oct 19, 2022 at 21:09
• @NautArch Just curious... and I know they have come out and more or less said to use colloquial English definitions in the absence of a game definition of a term but why can we not default to real world calculations to answer questions about problems that mimic real world situations? Other than the obvious "They didn't say we could..."? Oct 20, 2022 at 1:49

## No way to know

It's impossible to guess what the designers were thinking, and there have been no statements that I'm aware of that address this question.

Realistically, the whole concept is absurd. Even if we accept the historically unsupported idea that barrels are of standard size (even in systems where a Barrel was a defined unit, it has had multiple variants such as the Wine Barrel, Beer Barrel, or Oil Barrel, each with its own unique volume), the idea that a bucket is a standard measure is entirely silly. These numbers are, at best, suggestions and hand-waves and should probably not be taken too seriously.

For myself, I've always struggled with cubic foot measurements; without grabbing a calculator I couldn't possibly estimate how much stuff fits in a 4 cubic foot space, and that's ignoring the actual geometry of the storage space versus what you're putting in it. Technically, a steel rod 2 inches wide and 40 feet long is less than 4 cubic feet, but obviously that won't fit in an ordinary barrel. But would it fit if I cut it into 3-foot lengths? Heck if I know.

• I don't think "no way to know" is a helpful answer to a designer intent question. Leaving this unanswered is likely a better option than answering with a shrug - especially only 5 hours after the question being asked. Oct 19, 2022 at 16:07
• I think this is more than 'no way to know'. The important thing I take away is 'who cares' and that is exactly the right attitude to this kind of question. Just guestimate and be done. Oct 22, 2022 at 11:48
• @SeriousBri I don’t think “who cares” is a good answer to any question. The asker clearly cares or they wouldn’t be asking, telling them “i don’t know, who cares” is less than helpful. Oct 23, 2022 at 22:23