At some point in the near future I'm going to be in the possession of a number of laserdiscs (Mainly of the Japanese OVA variety), but of course in my excitement didn't really think about where exactly I'm going to put them. So as another example of my insessive need to make something slightly more grandiose than a prebuilt solution, decided to build a custom wooden open faced box to keep the LD's in. Being that I don't have the LD's in hand yet, I only have a loose "12.25in x 12.25in" to go off of as far as sizing goes (And I'm not even sure if that's accurate, or if that's consistent between US and Japanese releases). That does nothing for the other dimension, or any box sets that I might get in the future for that matter.
As it stands right now, the internal volume of this hypothetical box is 12.5in x 13.5in x 13.5in with the 13.5in's being how deep and high it is.

So, TL:DR,
A: What are the dimensions of a standard LD release? (And if there's a difference between Japanese and US releases, what is the difference?)
B: What are the dimensions of the largest box known box set? (Size wise, but disc count and physical packaging size tend to go hand in hand...)

Thanks in advance!

There is no standard. Single discs are the same as here in the US, logically, but the big boxes can be all over the place in Japan just like the US ones. The pasteboard used to make these things is the same as in the US, about 1/8", but the construction is all over the place. There are other factors as well.

For example, something like the original Gundam TV series. This show is sold in halves, with each half being a double slipcase. Meaning, 6-7 discs go onto a slipcase. Then another slipcase goes over that so that the LDs are completely secure. This is typical box construction for mid/late 90s Bandai Visual (Pioneer usually thinner, Toei thinner still) however those that preordered the set and/or got a first print of the first half also got a big box that would hold both half-boxes. The end result is a box that will just barely fit in my IKEA shelf, but only if it's laying on the right side.

Then there is the issue where a lot of JP LD boxes still have their exterior "shipping box" included because it does such a great job of taking the dings that would otherwise land on the box set proper.

It's best to shoot for 14"-15" to be safe. It still won't fit that dumb US Fantasia CAV set because nothing will, but it will fit almost every JP release since they at least mostly decided on "square" as a proper shape even if the number of cardboard layers may increase or decrease on a case by case basis.

I know for a fact I'm not getting Fantasia, and the only box sets that spring to mind that I know I'll probably get is the Star Wars: Definitive Collection & one of the Signature Collection releases, and other than maybe Nadia: The Secret of Blue Water and Urusei Yatsura as a absolute stretch (The latter of which wouldn't be in this LD box anyway, way too big...) I cannot see myself getting any other LD sets. From what I've seen all of those releases are bigger than a single disc jacket, but not significantly so. I was really hoping not to have a bunch of dead empty space (Over 1in) above the single disc jackets just in case one box set winds up being absurdly tall.
I know that physical dimensions aren't a thing most people take note of with release info, but it seems all the more nessissary when the format itself is a foot wide.

Well, I guess you'll have to wait until you own every disc you're ever going to own and then build the shelf.

Or just decided that a 1" gap doesn't matter when you have 1000 hours worth of LDs to watch. Frankly, I could not possibly care less. If something doesn't fit on a shelf, I put it on another shelf.

For what it's worth, the IKEA Kallax is about 13 1/4", and like I said it fits almost everything including that big Gundam box as well as a Ghibi ya Ippai in its shipping box, although only on it's side. Aparently it's taller than wide.

The Nadia box, by my measurement just now, is 13 1/4 inches tall, & the Gundam mega-box Zeta mentioned (I just received mine in the mail last week) is 13 3/4.
For what it's worth, I use Elfa shelves with a gap of 11 vertical spaces, which works out to 14 1/2 inches.

So it seems like 13.5in's tall seems to be a good height, as long as I'm cool with the most absurd of boxsets being delegated to sit on their own to the side.

For the sake of reference, here's a mockup as it stands right now:

(13.5in tall on the inside, 12.25in x 12.25in x .125in laserdisc sleeve.)

Nice. I couldn't even fit my 1980s Gundam in that though. LD, if you get really into it, requires serious space. Space and strength!

The tallest box set I got is the Urusei Yatsura set. It measures 335mm in height, just one mm or two too high for the IKEA Kallax shelf. Other boxes in the same height is Maison Ikkoku and Gundam Mastergrade box. Personally I prefer to have a little room above the LDs, a bit easier to get in and out of the shelf.

Anime on LD is usually really cheap (shipping excluded), and fun to collect. I just love the packaging done, nice artwork, extras, and sometimes just ridiculous oversized box sets. The bigger the better is my motto! As signofzeta said, you will need a lot of storage space that is heavy duty.

If you put two of the boxes you are looking at and run 2 1x6 inch white pine boards (or whatever wood you like - white pine is cheap and takes a stain really well) on both the top and bottom (to whatever length you like) you will pick up some more space for box sets on that shelf. Most of my lasers are stored on such shelving except I use record crates which I have slightly modified. (I also will build those crates from scratch when I need some - they are getting hard to find since the demise of records as a mass medium.)

The Mastergrade Box will fit in a Kallax, mine does.

All those cubes aren't actually the same size, you see...also, most box sets aren't %100 square. Sometimes they fit better some ways than others. I can't explain it, but some of those boxes will fit in some cubes and not in others.

If anyone can benefit from it, feel free to browse my collection. Everything in it will fit in a Kallax except that dumb US CAV Fantasia.

Oh wow! It seems like Urusei Yatsura would fit in there with just enough room to spare height wise. Probably wouldn't do it though, there wouldn't be any room for anything else!

If and probably when it gets made, I'm going with the 13.5 in height. It seems that only a really small handful of titles exceed that height, and width that isn't either Urusei Yatsura or all of Sailor Moon (Not that I would get them, just size wise.) shouldn't be impossible either. (And also trying to source 14in wide boards is going to be fun in and of itself, would rather avoid having to glue boards together to make larger boards if I can help it.) Depth wise things seem to be fairly standard, right? Now if only the titles I ordered would finally get shipped...

You're right, measured again now. My Mastergrade Box is 1mm shorter than the Urusei Yatsura boxes, so it should fit. Though, it will be a really tight fit.

I keep my big box sets on the top of my shelves. The only big boxes I have in the shelf at the moment is the Neon Genesis Evangelion movie and TV series box sets.